Last tried this a couple of days ago.
I see now that what I've always thought of as "channels" is called Teams, no idea how I've overlooked that for over two years but there you go.
My point is in Discord I can be on a dozen different servers with different administrators and seamlessly go between them. Not so in Teams. I'm stuck to one tenant (team) at a time. Which sucks if you need to switch between them.
You are correct that Teams today does not support Multi-Tenancy but that is really not an issue for 99.5% of organizations who would only ever have 1 tenant anyway
Teams is structure as
Tenant -> Teams -> Channels
Anyway, up until this became an issue, Teams has worked quite well. It does what we need when we need it, so can't complain really.
This was largely fixed, you may have to enable the "new meeting experience" though, which starts your meeting / call in a separate window from the main client