Federation has its downsides though, there's less cohesion across the board. A lemmy/kbin platform may have 20,000 users (an example) but most of them might end up with interacting on instances outside of the one they signed up on. Whereas everyone on Discuit, for instance, will be only interacting on Discuit. There's something to be said for how a userbase is spread, not just the amount of users.

Although in Discuits case, yes, it is really, really basic - and that more than anything likely stopped it growing before anything else.