There's nothing concrete that Discord holds that makes them remotely better for the users. Discord isn't even mutable, can't be heavily changed or swayed; it's someone else's closed proprietary product. Where-as Matrix or XMPP or irc can be bent, extended, changed to do more, to meet users where they are.
I don't know how any of these assertions that it's Discord or bust are made. This is an article of faith that Discord is simply the one and only way to go, or else, and the tautological definition of an article of faith is that which relies on no external support to maintain itself.
I do think there's a lot of possibility to figure out how to better bring users onto matrix or XMPP or irc, with easy to use web clients & better feature sets. But I also think culture shifts because culture does. For whatever reason there's doctrine that Discord is how it's done, and it's easy as fuck, but if we tried doing other maybe this Discord manifest destiny would not look so horrifically locked in as it is. But that would require not accepting the dogma of Discord crit-hype, that would require multiple folks trying.