However I use Beeper all day every day, via their iOS, Android, and macOS clients. Beeper (not the iMessage app, but their previous and continuing multi-network app) is pretty great. I get one consistent UX across all chat networks I use. Sometimes the networks drop out, but rarely due to Beeper issues.
Beeper is essentially a Matrix homeserver, plus a bunch of hosted Matrix bridges, and as far as I can tell, that whole part of Beeper was a great technical decision. The Beeper clients started off as forks of the Element clients, and honestly they were a trashfire at the beginning, but Beeper have been quickly iterating and replacing parts, and they're now pretty solid. They're not yet WhatsApp quality UX, but they're approaching it.
I don't think the problem is Matrix.