You can compare pros and cons of both messengers here: https://www.messenger-matrix.de/messenger-matrix-en.html

Post quantum encryption will probably be an issue in a couple of years and I think there will be solutions then in many messengers.

I am not sure what you mean by persistent user ids. How much would it matter if you run your own server line I so with xmpp?

I am all for using the true and tested xmpp protocol.