One of my longer-term goals is to integrate Mumble on XMPP (others have thought about this too) since its chat is pretty shit & needing accounts to join isn’t great but or two good foundational protocols.
XMPP is better for modularity which is why everything is at extension with means the foundations are simple & easy to implement where you can build something optimized & bespoke on it like Fornite’s coms or Nintendo’s presense. It’s a little harder to understand tho since out of the box you get almost nothing—but the big servers intended for chat like Prosody & ejabberd have sane defaults.
The centralization you are referring to seems more a client issue since the protocol & servers already ‘do the things’ but it sounds like you want a single ‘app’. For community building where you consider group calls less common, both Movim & Libervia offer more than Element (note the other Matrix clients are lacking feature parity) since they both can do integrated posts like forums—where Libervia supports calendars/events too. There’s no reason a client couldn’t exist with Jitsi or Mumble integration.
Ultimately use the right tool for you—it’s just nice to dispel myths that Matrix has some special sauce or that predecessors can’t fill the same roles (while also using less resources in all directions).
You can’t just “open an issue” if you don’t have a Microsoft GitHub account or live in a region under US sanctions or censorship where you can’t get access to it. These are pillars of sand to build your community on that not only lack freedom for users, but access too & control for your own content + moderation.
Gateways don’t need to be the only answer too—even just mentioning an unofficial space lets those that don’t want their data harvest can hang out together under the same topic but away from those service (even if most of the chat log is public, unencrypted anyhow).
Developers of all folks should know better & know the issues caused by proprietary services. They should not plan for where users are now but where they want things no be in the future but there’s a myopic view of this is where the users are. They don’t even give folks a place to air grievances like you are suggesting.