That's true, but I think something like that should be the basis for both. Telegram has groups that require invites and groups that anyone can join at will, but they're the same underneath and in both cases these groups have an "owner". Now you only need to have a group like that (it's the default for most such style groups that exist today, for example, in

chachi.chat

vibe with your tribe

and a relay that allows anyone to join, but only if they fit some arbitrary anti-bot requirements.

What are the requirements you're working to? My intuition is to start off with one relay per community, with relay selection options for that. Easy to work with, can have multiple communities of the same name. The moderators configure who joins through configuring relays. Its a base case that most are familiar with, and higher granularity can come as needed.

Authorship vs. Authority. Curation vs. moderation. Being able to fork a group's identity, and just port it somewhere else is incredibly interesting from a curation perspective. as long as there is a space, where people can meet randomly, basically open public microblog relays, there will be avenues for two branches of one group, living on two different relays, to interact in their intersections.