I’m looking into hosting one of these for the first time. From my limited research, XMPP seems to win in every way, which makes me think I must be missing something. Matrix is almost always mentioned as the de-facto standard, but I rarely saw arguments why it is better than XMPP?
Xmpp seems way easier to host, requiring less resources, has many more options for clients, and is simpler and thus easier to manage and reason about when something goes wrong.
So what’s the deal?
Most Matrix bridges to commercial chat systems also require accounts on those networks. That’s the only way to make them work on most of these systems.
I guess you are specifically referring to the Matrix to Discord bridge that does work like you describe, but a similar bridge has existed for XMPP to Discord in the past but is currently broken and unmaintained. The currently working XMPP to Discord transport does require you to puppeteer a personal Discord account, but that is rather because of a different focus of the used transport framework than any technical limitation of XMPP in that regard.
All platforms that don’t have public API access will require a way to relay that information, but I was talking about the difference in how the messages are relayed. Matrix bridges work fundamentally on each platform/protocol having its own room and relaying the messages through the bridged room instead of the user as XMPP does. That’s why you can relay the same messages to multiple rooms on Matrix, but can’t do the same on XMPP.