Are the latter points true? I mean, I personally do not like using Slack at work, but I have to admit it has a lot of really smooth UI and Product features that seem polished. I don't think I encounter bugs on a frequent basis at all, and my coworkers don't seem frustrated by using it.
I can second this, and I have a bias against it. When it came out I couldn't wrap my head around why people were excited about it. I've used IRC for like 20+ years and I didn't see it as much of an improvement from IRC.
However, I currently use it every day and honestly have no complaints. I still don't know why a chat app is worth so much, but it does what it's supposed to (lets me talk to others in my company in a single place), and basically everything you could think of has an integration for it. I haven't had an even remotely annoying user experience since the early days, and as a "slack hater" I've been actively looking for things to complain about.
But I guess I'm just one point of anecdotal data?