Agree, unfortunately. Zulip is one of those apps I want to see succeed but I cannot for the life of me get used to the UX.

Huh, I have the opposite experience, I love Zulip's UX. The fact that everything is a thread in a channel means I can quickly skip the threads I don't want, and I don't have to mark things as read in an all-or-nothing fashion. Slack doesn't let you do this, if you read a channel, it's now read, and you can't say "actually, keep this thread unread for later".