So, I have a Threema license, but from what I’ve seen its encryption isn’t post-quantum. Signal’s encryption seems the strongest. I host my own matrix server.
Also, I kind of don’t care where the servers are or which provider it is. Everything is encrypted anyway.
I mean if you acknowledge that user names can be used like any other website then your point doesn’t work. They don’t need my phone number. Most applications don’t need it but they do? Come on.