XMPP is not better than Matrix. My major gripes with it are OMEMO and the clients that implement different subsets of the extensions.

OMEMO still is an extension instead of the core. It should be extremely easy to upgrade a chat to an encrypted one but if the client doesn't have a plugin installed to support it, you're stuck with unencrypted traffic.

And the clients I've tested have all been visually unappealing and lacking in features. Reacting to messages, quoting messages, using threads, encryption, and finding rooms has been difficult or impossible with them.

Matrix has a major advantage over XMPP in that it has an official, reference client which implements just about everything. It works better than most any XMPP client I've tried and, this is my feeling, every MSC accepted by the foundation has actually been implemented, instead of just being suggested and"left as an exercise to the developer".

Matrix didn't come out of nowhere and didn't supplant XMPP for no reason. XMPP simply doesn't have the ecosystem that makes it attractive to users and debs alike.