You’re right that most of the things I mentioned that Matrix can do (but telepathy can’t) are also doable with XMPP. However, architecturally/ideologically the protocols couldn’t be more different. In Matrix, conversations are always shared over all the participating servers - this is really important from a data sovereignty perspective. A given conversation should never be anchored on a single logical server. In Matrix, conversation history is a first-class citizen: in fact, Matrix is only about synchronising conversation history between devices. It doesn’t even have a way to do simple store-and-forward messaging like traditional XMPP. Similarly, E2E encryption is a first-class citizen, baked into the core protocol (albeit still in its final stages of development), rather than an afterthought extension like OMEMO. As a result, the entire protocol revolves around supporting E2E-by-default (eventually). Finally, the model of the Matrix spec is a single consistent monolithic spec published by the project, rather than the cloud of XEPs which characterises XMPP. This has advantages and disadvantages, but provides a completely opposite approach for those who want it. This is what Matrix brings to the table 
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