Mastodon got so much better for me when I left the generalist instances. I now see my instance as a micro community with the ability to connect to a greater community.
Each instance has a local (instance) timeline and a federated timeline in addition to one's own personal timeline. The local timeline only shows posts from accounts on that instance. The federated timeline shows posts from all accounts followed by at least one user on the instance.
So these two timelines can be dramatically different and they're a big factor in account discoverability and the "feel" of an instance.
Of course you can go out and follow ~anyone from ~anywhere, and that's the Fediverse's killer feature, but the more local content matters too.
Also it is not 100% true that every post bubbles to every instance because instance admins can blacklist other instances.
(but didn't find anything local or interesting...)
Once you see something annoying from someone you on your feed, just unfollow that person and you'll have a very non toxic feed.