As someone who has written and maintained a RSS aggregator for years, I can tell you that this jankiness is in big part because of how vague and under-defined the feed formats (RDF, RSS2, Atom) are, and how "creative" various websites are in producing feeds which are just barely standard-compliant, but also just enough screwed up to cause problems when parsing them.
It was a headache after a headache trying to get all the weird corner cases handled.
I've been using Matrix for several years now, and am very happy with it, and with the progress that it made.
I have one instance just for me, which I use for general chatting, as well as for some light experiments (I'm toying with some client development and trying new plugins or appservices now and then).
I have another, private and undfederated instance for family comms. I set it up at the very beginning of the Covid-19 era, when nobody knew how long and how severe will the travel restrictions be, and we've been using it heavily ever since.
Something about books, covers and judging...
It's been in beta for a while now. Here's the blog post introducing video rooms: https://element.io/blog/drop-in-drop-out-chats-with-video-rooms-and-a-new-search-experience/
Mastodon does not need to scale well. Even if the userbase shrinks to what it was before the Big Twitter Exodus (or whatever you want to call it) of last year, it will be perfectly alright.
Mastodon was fun and enjoyable before. It does not need more users to remain so.