Then once the rss ecosystem had been largely wiped out, google killed reader. Sure you could migrate your data out, but to where? It took time for replacements to get to maturity, and they lacked syncing or financial backing that made them free. It was _possible_ to get an alternative, but the overwhelming majority of people are not really able to deal with the immediately available alternatives, and by the time the RSS ecosystem had redeveloped usable software the majority of the people who had been using reader/RSS were no longer going to switch back because they'd migrated to other systems.
The cheaper/free service to drive competitors out of business model is a tool monopolists use all the time because it is effective. In this case google did exactly the same thing, honestly I don't think out of malice, and then realized that they couldn't make a profit of it and so killed the service. But fundamentally their actions were the same as the monopolists, and had the same impact, so when they shut down reader they basically ended rss for the vast majority of users.
For example, NetNewsWire was a good piece of paid commercial software which I used for years, that was essentially killed by reader because they simply couldn't afford to develop or support it when the major competitor was free. NNW is now free and OSS, but that was after the IP became functionally worthless and the company that had bought it simply returned it to Brent Simmons (the original author).
I feel sure there were others but would have to look them up.
To summarize, yes. There were plenty of mature alternatives and a migration was easily done by exporting and importing a file. Feedly supposedly got 3 million new users in the two weeks that followed Google's shutdown.
A far bigger issue than Google shutting down was the fact that people had moved on to Facebook and Twitter while newspapers created closed ecosystems with their own apps. Jason Kottke, then one of the world's most popular blogs, declared blogs to be dead.
The result of this was when reader shutdown the overwhelming majority of users simply stopped using rss, presumably even if they did export their subscriptions they've long since lost them, and built up habits around non-rss based mechanisms. Hence rss (for anything other than podcasts) ceased being relevant for the overwhelming majority of people.
I'm trying to make it clear here, the issue isn't that using RSS became impossible, it's that by making reader free google decimated the rss reader ecosystem such that when they killed reader there simply weren't practical alternatives for the majority of users of google reader. As a result reader being killed changed the general habits of those users to no longer use rss feeds for information, and given by that time things like twitter provided similar services (most blogging platforms have a "post updates to twitter") they had no real reason to go back to rss readers.
So the basic argument for reader making rss become irrelevant for general blogging, etc was:
1. RSS comes into existence
2. Apps start being made to subscribe to rss
3. People start using those apps
4. Google introduces Reader, which is free
5. Paid apps from <2> can't compete with free so either die or adopt in app ads (which at the time reader didn't have) so people move to reader
6. Non-google rss readers don't have syncing, so people move to reader
7. Non-google rss readers either require people pay, or use specific paid services, to get syncing, so people move to reader. Or they use google reader as their back end so their users can now trivially just start using reader anyway.
8. At this point there are no major alternatives to google reader, it makes up the overwhelming majority of all people using rss, as a result the few stand alone readers that still exist are for niche use cases or are unpolished hobby projects that come and go over time
9. Blogging platforms introduce tools to allow posts to blogs to automatically post updates to twitter, Facebook, etc
10. Google kills reader
11. The free rss readers that still exist all use reader for syncing, so lose syncing, and have to either charge money or require users adopt paid syncing tools, so people don't migrate to them. The projects that come into existence at this point are too rough for general users so they don't bother, and at this point they don't need to as the autoposting from <9> means that they don't need it.
I think that's a fairly fair assessment of what happened. But I think there's a big caveat to be addressed though. Google reader was far and away the most popular RSS reader, like overwhelmingly so, prior to it existing the market of RSS readers was something where a few people could earn some money, but it was not really a significant market. So my question is, absent google reader would RSS feeds ever have become as popular as they were during the period reader was available?
My _feeling_ is no.
That's exactly what I was referring to. There were options, I was using one (for years at that point in time).
However, the problem was a missing synchronisation of readed entries between your home and office PC. Mobile device was not a thing back then but slowly started main stream adoption. I mean, very few had smartphones.
Google reader was revolutionary, solving this exact problem for free and mobile app quickly followed. It caused almost all offline RSS readers to decay and starve to death.
And then few years passed by, and this is the moment they pull the rug, but the damage was done. Luckily, Feedly and others quickly emerged, and smartphones were a thing. Also, some self hosted RSS readers came to existence and get polished.