In XMPP, e2e encryption (just like everything else) is an optional extension. So in practice half the clients don't support e2ee, half support different version of e2ee (can't talk to each other) and pretty much all e2ee are likely full of holes since there are too many implementations to review.

In Matrix, e2ee is in a library that all clients can use, so while it is not Signal, it provides decent security.