Matrix has absolutely bonkers resource requirements relative to the end user experience it delivers, and can be much more complex to deploy. Some of that is intrinsic to federation or to its protocol; some is related to Synapse specifically. I'm not sure whether competing server implementations will catch up before Synapse gets a rewrite in a more performant language, but I'm eager for one or the other to happen.

I admin a public Matrix server, so I'm not by any means against the product, but IMO there's a reason it hasn't meaningfully displaced XMPP yet.