On the other hand, I don't think anyone accused slack, with multi-megabyte webpages and even worse mobile app, of being a great experience. I think I used it once, and said no more.
I've met only a few programmers IRL that complained about slack, and even then it was for ideological reasons, not user experience reasons. Everyone else, most programmers and all non-programmers I know like the user experience.
I haven't had any real issues with desktop or mobile apps either.
I use Slack for work, and while it was an order of magnitude better than the dumpster-fire of Hipchat (which it replaced for our team), I still think that the interface is kind of "meh".
Custom emojis are fun, inline markdown is useful, but it takes a lot of memory for something that, to me, seems like it should be lightweight. We've had IM since the 80's, after all. There's a part of me that has a visceral reaction to seeing an IM client taking more than 100mb of memory (though to be fair they seem to be getting improving that a lot.
The Electron-ness and memory usage of the app on desktop are certainly annoying, but the UX is still far better than any terminal-based or open source GUI for IRC. It was better than HipChat when my company moved to Slack 4 years ago.
Overall Slack is a net UX improvement over everything that came before.
I'm not sure what about the experience you had a concern about. Slack is the de facto user experience standard right now, with everyone from discord to teams copying it.
They do. Non-engineers just tend to blame the age/quality of their company issued hardware rather than the problematic software causing performance issues.
