That's one mechanism, but another mechanism is what I said - an open system fragments too much, making it completely unapproachable. Or even within one "vendor" if they can't make up their mind about how it should work (i.e. if they can't be opinionated) it's just as bad as being fragmented.

If there is still one company pushing their own strongly opinionated client, how does having competing options available to power users detract from that? Like I'm not saying Signal-the-client should go away, rather that Signal-the-company who runs Signal-the-server could be accepting of third party clients, to the point where Signal was easily usable from F-Droid and whatnot. How would that undermine the mass market option?