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.

?

Could you elaborate?

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.