I don't believe it's any of those things. Though, certainly the ergonomics of a traditional studio, and the equipment therein, works best for engineers who learned in those environments and using those tools. Those engineers happen to be the most experienced engineers working, so they are probably, on average, better than most younger engineers with much less experience.
However, the reason some of the classic records sound amazing today is because they cost hundreds of thousands of dollars to make, in a time when hundreds of thousands of dollars was a lot of money. This is reflected in the rooms where they recorded. The quality of the studio itself is every bit as important, maybe even more important, than the equipment within it.
When recording live musicians, a bad room literally cannot be overcome with good equipment. And, thus, simulating a great room with equipment is harder than simulating a great console, or a great EQ, or a great compressor. Digitally removing the room "badness" and putting in "goodness" isn't something that people have even really tried.
Records made at Abbey Road studios sounded great because the room sounded great, the microphones sounded great, the board sounded great, the EQs and compressors sounded great, and, the musicians sounded great playing through their great sounding instruments. They had everything working in their favor, and that moment of everything coming together nicely was captured by excellent engineers.
So...the reason most records don't sound as good as Dark Side of the Moon is not merely that there aren't a lot of consoles comparable to this one. You could probably find something that would be a sufficient substitute (and maybe even a laptop with a very good AD/DA could substitute for much of the equipment in a studio). But, any mediocre piece in the chain, starting with the musicians and the room they're playing in, will make a mediocre recording.
Pink Floyd, a very talented bunch of musicians and songwriters, had a massive budget, a truly inspired bunch of songs, and a lucky bunch of connections in the industry to get them the best people and the best gear all in the best studio in the world, and the result is a classic that sounds better (by some definition of "better") than 95+% of big budget records even made today. There have been similarly high quality recordings made, but it's rare...and I don't think a specific set of equipment can do it (after all, lots of other records were recorded in the very same studio and didn't sound that amazing). A lot of stuff has to come together for it to work out that way.