That was possible on Reddit too. Every single sub with overbearing mods could have been replaced at any time with an alternative. A bunch of alternatives tried to get off the ground, some succeeded more than others, but most never overcame the original, if they ever picked up at all.
It’ll be the same way here. If the community doesn’t leave the original home because they’re “settled there”, alternatives will not grow.
This entire migration from Reddit should make it it very, very plain how utterly impossible it is to get large groups of users to move. Reddit is all but whipping them with jumper cables right now and they’re still using it.
You can’t just expect communities to move because the admins suck. You have to actually attract them there.