Underrated benefit of lemmy is like minded people will tend to join the same instances and if I don't want to interact with those groups I can just filter the whole instance.
A lot less annoying then endlessly filtering content by community and user
No, anyone gatekeeping Lemmy users who aren't on the largest instances are fundamentally working against how the fediverse is supposed to work. lemm.ee is smaller, and generally politically neutral, but it also seems to properly moderate hate speech, violence, harassment, and illegal content. As long as that persists, all should be good.
If it ever comes to a "be on .world or you're sus", then .world can just disable federation and become Reddit 2 while the rest of Lemmy embraces decentralization.