There are already a bunch of native Teams/Slack/etc.-like applications. Matrix has a good number of native clients[1]. There's Ripcord[2] which supports both Slack and Discord. There's Matterhorn[3] for Mattermost.
What I want, is something that ISN'T a poor copy of Slack. We've lost the rich landscape of differing chat/collaboration clients, and now just have a mono-culture of Slack-Clones.
That isn't true at all - Matrix has a rich and growing ecosystem of chat clients. For Slack clones, you're well stocked, but the links given to you by the parent shows there is much more out there.
[1] https://matrix.org/clients/
[2] https://cancel.fm/ripcord/
[3] https://github.com/matterhorn-chat/matterhorn