Yes, there’s an ecosystem, but it’s neither extensive nor mainstream. Feed readers are hit or miss, and I haven’t found one I like. Subscribing to 50 people is enough to make the feed unusable since there’s little to no organization.
While this isn’t entirely the protocol’s fault, its poor state is largely due to its lack of mainstream adoption—too few people care about it. The protocol itself might also be part of the problem.
So discoverability is still a problem because not enough people care about the existing solutions.
It's only for Firefox though because I like my reader being integrated into my browser and Firefox was the only one that supported a sidebar at the time. Looks like Chrome supports sidebars to now. So mayhaps I'll update it.
What kind of organization do you want? Every feed reader I've ever used let me categorize/organize feeds in whatever way I wanted, but it's a manual process.
I'm also not sure what fragmentation has to do with anything. I don't think I've used a feed reader that didn't understand all current flavors of RSS and Atom, so it makes absolutely no difference what the webmaster decided to use, my news reader can figure it out.
It is a little bit annoying when the webmaster doesn't put the full text of the article in the news feed, and instead wants you to actually visit their site to read their stuff. I'd guess that they do that to make sure that you actually visit the site once in a while and might accidentally view an ad so they can make a few cents or they hope that you might see something else on their site you might be interested in or whatever. It also saves some bandwidth by not downloading the full text of an article if it turns out that I wasn't interested in it.
I can't speak for others, but as someone who hand codes my HTML, it is a non-trivial amount of work to convert the entire text of a page into an RSS feed, whereas it is easy to add the headline, datetime, and summary.
I get that it is pretty cool to read stuff inside an RSS feed reader, but doesn't fit with my current workflow. My site has no ads, tracking, cookies (aside from the ones imported by the odd embedded youtube video).
It rather depends on the amount of content the RSS _author_ includes in the RSS feed. There's nothing in the RSS/Atom protocol that prevents you from reading the entire article, but some website creators decide to truncate the feed content.
My RSS reader of choice, InoReader, has the option to download the original website which solves the problem. However, I have over 200 feeds and it's rare to find one without the entire content being included.
Anyway, services like Feedbin have been going strong for a long time, have a rock solid syncing system with great tools for things like seeing frequency of posting and abandoned or moved feeds, folders, automatic filters, and broad support in the app ecosystem if you don't like their apps or web experience (which is very good).
RSS is absolutely extensive and has millions of users. It's at least as mainstream as Mastodon/ActivityPub, it's just not talked about as such, and that's _excluding_ Podcasts as a use case.
I’ve emailed many technical writers whose work I liked, asking them to add feed support, and most didn’t bother. One possible reason could be the protocol itself and the fragmentation between RSS, Atom, JSON RSS, etc.—or it could be something else entirely.