Eh, i disagree. If i have the option to join a niche community or be external to it - i feel you just made an argument against federation. I should join the community, so that i'm not arbitrarily blocked for reasons out of my control. If i get kicked out at least i'll know, and it was likely due to my own actions.

Ie imagine mastodon.art has a good Blender community. I'm joining Mastodon for exactly that community. If i join mastodon.social, i may as well .. not. It's blocked by mastodon.art. It's not even worth my time signing up if my goal is to be part of a specific community.

I'm not trying to build a general audience or have my general posts heard by the public. I'm trying to be part of a specific community. Federation seems bad here, if the community you're interested in is not fully open at least. As mastodon.art most certainly is not.