Any and all new information that can be gleaned from finds like these about the ancient Canaanites that once influenced our Celtic, Iberian, Germanic and Roman ancestors is interesting.
For instance, there would have been no census to bring Mary and Joseph to Bethlehem, there would have been no Pontius Pilate. Crucifixion itself was a favored means of execution in the Roman Empire, and may not have been employed by whatever political entity that would have been dominant in Judea in its stead.
The earliest accounts of Jesus were written only one generation after Jesus's death. Plenty of first-hand accounts were still available. There are many of corroborative accounts of Jesus and other historical accounts of this period.
Christianity had spread to Greece in 50 AD, only 20 years after Jesus's supposed death. In an age where information moved so slowly, it's remarkable that Christianity had spread so quickly.
It's fair to dispute the details of the canonical/apocryphal stories—surely those are contrived—but the idea of Jesus had to come from somewhere. No one else was interested in taking the credit, which should tell us something.
What present-day meme will reach a similar level of distribution and hazy origins? Will we see future generations speculating about the true nature of Harry Potter, or the Jedi, or Chuck Norris's superpowers, or the one true Nyancat?
In short, it's highly unlikely Jesus is purely fictional, and there was almost certainly someone known as Jesus executed by Pontius Pilate. Is this going to make a difference to your beliefs in any direction? No.
Those writings are doing a lot of heavy lifting, since that's about all apologists can hold up as 'contemporary corroboration'.
Antiquities was written in the last decade of the first century, so at the further end of your 50-60y range. As you note, the wording in the Jamesian reference is not very compelling in itself, and historicists generally argue that Josephus would have explained his terminology much more carefully than we see in that section, so there's some reason to doubt it was in the original.
The longer section from that work that apologists refer to is clearly an interpolation. The style is completely wrong for both the author and the context. The previous pages are describing taxes, protests, massacres, etc and then there's this very brief and spectacularly flowery prose that attests to Jesus being the Christ, and to the ten thousand wonders he did, and then on the next page the author continues with 'And another terrible thing that happened to the Jews ...' -- which only makes sense once you remove the clearly forged / added page.
At which point we're really short - a rounding error away from zero - on any corroborating stories from the 1st century.
Yes, Mithras, Dionysus, Zarathustra, and other pantheonic cults have quite a bit of similarity to the messianic figure at the center of Christianity as well as its early rites and rituals. Whether Greek, Iranian, Phoenician/Hebraic fusion doesn't really change the convergence that arose as a consequence of the Roman policy on toleration of local cultures.
Mithrasism was a good candidate to replace early Christianity, as they were rival religions. Christianity persecuted Mithrasism starting in the fourth century CE, all but wiping it out.
Information would move quite fast within the Roman empire, especially in the Mediterranean basin. There was a neverending circular movement of goods and people there. Soldiers, mariners, businesspeople, bureaucrats, learned men. Getting from Roman Palestine to Greece by ship was probably faster than getting from Roman Palestine to interior Syria by caravan.
The earliest allegorical story that mentions the character was written around 70 CE - so a good 40 years after the supposed crucifixion.
You assert plenty of first hand accounts were available (they weren't), and that there are many corroborative accounts now (there aren't).
The movement seemed to be spreading remarkably slowly until it was leveraged by an opportunistic emperor in the early 4th century. At that time there were dozens of various sects, the Nicene was just another variant, but the orthodoxy that came out of that adoption meant we lost many of the works and details of the others. That rewriting of history would also address your last point, too.
The Bible says in Galatians 4:4, that "when the fullness of time had come, God sent His Son." Thus, when Jesus was born and what was going on was not happenstance. The point in history and the circumstances of when it happened (for example, the Romans being in power, and their use of crucifixion on wooden crosses) were foundational to Him accomplishing the work the Father sent Him to complete. He had to be raised up on a tree at His death in order to take the curse of the sin of His people upon Himself.
I'm not Jewish, I simply loved the consideration regarding how history might have evolved differently.
Most historians agree there was no such census, certainly not one that required people return to their birthplace. There was a 6CE census (but it certainly would not have required everyone travel to their origin - that would have been as ridiculous then as it sounds now), plus the timing would put it at odds with Herod's death in 4BCE. In any case, it appears to be a literary device employed by the author of Luke to get the main character of the story to the prophecy-mandated location.
I don‘t know about Christianity. I think that without the conversion of Constantine, Christianity would have at best been something like Baháʼí is today, a relatively small, persecuted religion. It was Constantine’s conversion and the subsequent adoption of Christianity by the Roman Emperors that made Christianity what it is.
Christianity without a powerful pan-Roman culture may have stayed as a kind of messaniac Jewish sect, confined to Jewish communities around the mediteranean.
It would have likely looked very different from this Christianity, possibly to the point that we'd barely recognize any similarity.
Why aren't Coptic christian sects more representative of what would have happened without Christianity usurping/inheriting Roman authority?
In a way, maybe Islam is closer to what you're suggesting. A monotheistic religion without the dominance of the Roman empire or influence from it, and without the rather odd violent debates about the trinity and the relationship of Christ to God etc. that went on in early Church
Some features of the winning religion seem convergent (e.g. intolerance to rivals). But I think expecting Christianity in particular would be like expecting a rewind of evolution to end up at humans.
Also the 'dark ages' weren't really as dark as some might think. Arguably most of the decline was a result of climate change and the plague, which lead to a collapse of urban populations, which were the centers of literacy and education. However technological progress didn't really stop, there were significant improvements in metallurgy and agriculture and by the high middle ages Europeans were much more 'advanced' in almost every area compared to ~400 AD.
The one thing ancient empires were exceptionally good was concentrating resources, e.g. no state was able to field a standing army in the hundreds of thousands and no city even came close to the population Rome had until the 19th century but that was due to political reasons (shipping tons of grain half across the (known) world to fed a massive unproductive urban population just to shore up some political support simply wasn't viable anymore).
In the east, in Anatolia, the Roman civilization lived on with quite a bit more vibrancy and power than people often recognize.
But in places like Britain it's pretty night and day: early 5th century still a predominantly Christian Roman province speaking Latin and Brythonic, by the end a predominantly Saxon speaking mostly non-Christian population with drastically reduced economic activity and wealth.
You can't raise taxes when half or more of the population is gone. As per WP: "Some historians believe the first plague pandemic was one of the deadliest pandemics in history, resulting in the deaths of an estimated 15–100 million people during two centuries of recurrence, a death toll equivalent to 25–60% of Europe's population at the time of the first outbreak"
And this is after a couple generations of political turmoil, other plagues, and invasions.
Also we don't really know Christian Britain was before the Saxon conquests, it's not unlikely that most British people outside of urban settlements were still pagan and only superficially Christianized. We also don't really know did the British people become culturally Saxon. According what was written down by the surviving members of the Romano-British elite it was a result of genocidal conquest. However the predominant view of modern historians seems to be that the process was much more peaceful and more akin to the Arabization of the Middle East and North Africa (i.e. the conquerors established a dual class system which incentivized the local population to adopt the Saxon language and culture because of the economic and social advantages. Also, unless the Saxons were significantly more brutal, oppressive and numerous than the Franks, Goths and other invaders this would imply that the local Britons weren't actually thoroughly Christianized since Christian populations were usually able to resist this type of Cultural conversion).
In regards to the comparison between Franks and Goths and Saxons, it's not really the same. In those cases they took over the existing Roman state and continued its administration, leaving the institiutions of civil society much the same and even adopting Latin as a language and Roman cultural practices for themselves within a couple generations.
By the time the Saxons arrived en masse in what is now England the existing Roman administration had pretty much collapsed. That seems to be the archaeological evidence in my recent reading: drastic declines in the economic vibrancy of British communities. Things like amphorae and other mediterannean trade goods vanishing. Rich people burying their wealth to hide it from invaders. And, yeah, the stories told by Gildas & St Patrick, our only real contemporary accounts from this general period, seem to agree with this: decline of local British power, retreating into small cloistered communities, Saxon (and other Germanic) raiders wea continual pest even in Roman times, yes, but after the departure of the Roman administration it becoming drastically more aggrivated, the locals were incapable of defending themselves, and the British turned to Germanic mercenaries as a defense (a common Roman tactic). Which predictably backfired.
I've read two books commenting on this period of British history recently, and both disagree remarkably on the degree of cultural and physical replacement. But on the whole the genetic and archaeological and linguistic evidence seems to me to support the statements by Gildas and St Patrick: the British were on the whole replaced & expelled (to Wales, Cornwall or Brittany), or exterminated. This is reflected in part by the fact that only a few Saxon settlements carried forward on top of existing Romano-British settlements, and most adopted new names entirely. Even some prominent ones like London were left pretty much uninhabited for generations before being re-settled later.
There is evidence that there was at least some degree of peaceful coexistence between Saxons and local British at least in the early periods of settlement. There are burial sites where both genetically British and German (or mixed) people were buried together, with identical grave goods and seemingly with no distinction. This would indicate that at least some local people adopted Saxon customs and language and were accepted as equal members of their society. However this is not exactly conclusive, there are also many segregated burial sites so the type of interaction between the local Britons and the German invaders/settlers varied by area and time period, it took them well over 200 years to almost fully conquer the territory of modern England.
Gildas and St Patrick were members of the Romano-British landowning elite which was displaced by the Saxons, I'm trying to dispute their authenticity but their experience might not have been representative of the majority of local people (who were never fully romanized or integrated into the roman society). It would not be completely surprising if local Britons decided that they would be better off by 'switching sides' and adopting Saxon/German culture. Of course we don't know how widespread and voluntary the process could had been, however according to genetic evidence it must have occurred to some extent.
But, yeah, unlikely.
I think most people would consider that a “dark age” or “collapse”.
However outside of that period it's not that straightforward. The Roman economy was stagnant or declining well before the Western empire officially collapsed. According to some historians growth in much of the Mediterranean region stopped with the Roman conquests at the end of the Hellenistic period. But even if we assume that ~200 A.D. was the peak can we really say that there was more technological innovation and economic growth between the 3rd - 5th centuries than between the 8th and 10th centuries? Probably the latter..
And it also varied significantly depending on the area we're talking about. Italy probably took the longest to recover but it's economy was massively inflated due to wealth transfers during the Roman period. However the center of economic and political power in Europe has shifted to the other side of the alps France and Germany had nearly the double the population in 1000 AD compared to their Roman peaks. And some places like mainland Greece arguably never did until the 19th century (it was probably was past it's peak during the Roman period as well, though. A similar process occurred in the eastern Mediterranean where the center of power shifted from the coast to the inland areas (like the area modern day Iraq).
And we're only taking about absolute growth here, per capita productivity probably wasn't as much affected and most of the decline in international trade (which eventually recovered) was balanced out by higher availability of land (per capita) and improvements in agricultural techniques and tools.
If we're talking about technological growth, well again in some areas like architecture the decline was severe and near total (most communities couldn't afford to maintain the buildings they already had). In other areas the reverse might had happened, based on archeological evidence the average quality of metal tools and weapons in Western Europe was already much better in the 7-8th centuries compared to what the Romans ever had. The heavy plow was introduced in agriculture, water mills continued to be built. Literacy rates fell, however that was to a large degree an outcome of the collapse of urban populations. However the link between economic and technological progress and education in the ancient world wasn't all that clear.
Once Rome fell, the educational system outside the Church disappeared entirely for almost a millennium and the Church remained the only institution that carried on the tradition of reading and writing in the West.
This must have had some impact on the tempo of overall technological progress. Just like the fact that the successor states, unable to concentrate resources as much, couldn't start big public works (channels, aqueducts) which used to require a lot of highly qualified people.
I don’t know if the facts actually back that up.
If the intelligentsia are focused on climbing fruitless political ladders steeped in theology versus scientific endeavors, you have less progress overall.