I’ve never heard of federated communities.

Keep in mind the fediverse is not lemmy. Lemmy is the software that allows you to read, post, and comment, but there are others like piefed.

The basic problem you’ve described is a potential problem, but in practice it’s not really significant.

I’ve never really cared much for the idea of “community” online and certainly on reddit. Like what is a community really other than a category of similar posts ? The idea that it’s the people that make the community and that you need one cohesive place or platform for that community to exist just isn’t accurate.

For example, every instance might have it’s own “selfhosted” community. If you search you’ll see a half dozen. Just subscribe to the few busiest like everyone else, and you’ll see all the posts. I guess what I’m saying is that “the community” informally exists across all instances.

The best thing about federation is that you can choose not to follow specific communities if you don’t want to support their content. Like maybe you’re into manga memes but you don’t want to support the lack of moderation on some instances.

I don’t know exactly how it works but piefed has a feature where if a post is a link to a news article then it will list the comment sections for all cross posts under one post. Something like that anyway, I’m not sure exactly how it works, but often when looking at a post for an article you’ll see comments from other posts of the same article.