Somehow we had like 15 users and not one of them managed to make a comment that wasn't a new thread - like I said though, it was like 2 years ago. Either there was a bug, or it was a design decision, or maybe even a misconfiguration on the server - regardless it got a hearty thumbs down by the community and we went on to try matrix. I was hoping for Zulip since it was a way easier install than matrix + riotweb was, especially since we wanted to self host everything. In the end all the bugs we had in riotweb and the phone apps were enough for us to jump for MM, which has its own problems but was most in line with what we wanted.

Anyway, if Zulip isn't thread-first, then I guess it's less a competitor to Teams than I thought. The only way we found to make teams work for us and our very small team is to keep everything in a named joint chat and everyone utterly ignores the channels like the plague. It's always amusing when someone posts something to a channel for the first time in weeks/months and then people start responding thinking it's chat and every. single. response. becomes a new thread, because they didn't respond inside the original thread.

That's very odd to me, I've never had that problem and don't see why it could be.

Zulip is thread-only, it's just that thread can be used as channels if you ignore the top level (streams).