Signal is fine for private communication. The advantage with XMPP services is that one can remain anonymous, too, and decentralized communication does grant some benefits.
However, I don't see value in asserting XMPP superiority. In somecways, it is superior. In others, not so much.
I do like JMP.CHAT, which leverages XMPP brilliantly to offer voice, SMS along with all the other capabilities of XMPP.
Using apps that cant provide anonymity and at the same time not the ones that do is very dangerous for society as a whole. Some journalist and activist need anonymity and if only place where they can be heard is on mainstream apps that don't offer anonymity, they are stuck.
It's a good thing we have the choice, isn't it?
There's a reason why people say XMPP and not list any actual apps. Conversations looks like it's from like 2014 and is the only usable app.
Could you elaborate?
He doesn't like them because they're centralized.