I disagree. Discoverability is to discover new stuff from new places you haven't seen before. In Lemmy, for example, I can sort by All/New and I'll discover lots of new things I haven't seen from new places. Interesting to me or not, there's discoverability.
RSS readers just fetch a certain .rss file from a website and render that for you. RSS is a simple tool, it's not even comparable to something like ActivityPub.
You also have no way of discovering new stuff, you have to find them yourself. Whereas with ActivityPub you can. Nor can you interact with the feed objects (comment, like, etc).
Is the last one real? Has any sane dev made something like that monstrosity?
It's not like the others are any better, but who would ever think of doing the last one and why?
Art and music class in middle school. Literally useless. Fortunately, we no longer do such useless classes in high school. I pretty much lived my life through middle school without friends, so I hated the art class even more because we sometimes got grouped together to make some "art".
Proprietary garbage