Earlier quoted context omitted.
Unpopular HN opinion: Teams doesn't suck. It's not as pretty/lovable as Slack, but it has an additional level of organization (each team gets their own set of channels), you can add tabs of related apps/sites to each channel, etc. As far as I could tell having used both simultaneously for a few years, Teams is a complete superset of Slack.
We use Teams at work, and for that it works quite well. Calls and desktop sharing work well, the channels do what they do, integration with OneDrive and the wiki thing is nice etc. But then I got a member of a different Team, for one of our customers, as part of some integration work. And boy is that a CF. Unlike Discord you either have this team or that team active. Notifications from the other are horribly unreliab…
AirSend gives you a few simple (chat, voice/video, files, tasks and wiki) but powerful tools and then get out of the way.