There’s no evidence to support what you’re talking about. Mastodon, Misskey and Lemmy monthly active users flatlined a long ago. They are not growing and there’s no evidence they will resume to grow in these conditions.
A multi-protocol network might not be unlikely, but it will still be very asymetric, with AP as a secondary actor. Power shapes technology, not the other way around.
If the protocol doesn’t give incentives for an even distribution of users, it’s not going to be solved by blaming individual instances or individual users.