No native proxy support (because it depends mostly on UDP and WebRTC), bloated clients (for the major part) and not truly decentralized (most users just registered on matrix.org's servers and seem to not even know about other instances or self-hosting).
XMPP has been out for years and supports different type of E2EE, from the widely known PGP, to OTR and the newest and most used OMEMO.
No web registration is required, you can do all in-client behind a comfy proxy (like Tor) :).
Mobile: Monocles [Graphene or any other privacy rom is highly suggested]
Proxies for mobile devices: InviZible Pro, should be runned in VPN mode [for desktop just install the Tor daemon for your distribution]
Get out of the Matrix (literally), be free from companies and bullshit.
From a cypherpunk.
P.S. calls on this instance are disabled for security reasons and because the server is still not capable enough. Might consider to turn them on in the future.
I got a video on XMPP too. animated… Another matrix vs XMPP one coming soon also. but this is on XMPP vs Signal and OMEMO vs OTR https://video.simplifiedprivacy.com/xmpp/