I am in the happy situation, that my employer values employee opinions. We use zulip. It's not perfect, but clearly more useful than Slack. The one complaining most is our CEO. But he is smart enough to understand that happy coders are more essential for a small SW company than a happy CEO.

The main failure of IT or computer science is the lack of open standards and federation. 40 year old Email was the last somewhat succesful one. You can use various clients like Emacs, Thunderbird, mutt, Gmail web UI and there is no need that sender and recipient share either provider or client.

In communism it was the central planning commission that decided what products consumers want to buy. Today it's Slack that decides how people do IM at work. And Google or Apple how people use mobile apps. Facebook how you interact with your friends. I hope that these monpolies/duopolies would share the fate of communism. How do we get there?