Neither you nor GP are articulating or giving examples. Start there and we can have a proper discussion, otherwise it'll be just another case of 'he-said-she-said'.
In case you are wondering, I don't consider the UX for IRC "good" (in a forum with "hacker" in its name, of course IRC will come up). It is good because it is open, simple and lightweight, but when you want a history and image/file transfer, and most people do, it breaks down and you need ad-hoc solutions.
Which is exactly why the IRC clones (Slack, etc) have taken off
The only thing that took me some time to adjust to was how overwhelming joining a new server can be. So many channels! Everything needs my attention! But after using it for a long time, I think this is actually a feature. I can mute channels and categories I’m uninterested in, but how many channels on Slack are never found due to poor discoverability?
We run both Slack and Discord at my work and the engineers vastly prefer Discord, for what it’s worth.
Caveat: It seems much more geared towards users who commit significant brain-space to the subjects they join (for example: catching up on threads is easier if you’re paying attention to realtime notifications), whereas I have a lot of interests and really just want the gems whenever I “sit down” to work with a particular interest.
Some people like this kind of constant distraction, though.
I could see Discord as made for power users where Slack and Teams would be aimed at casuals. But I do think that Discord does a pretty good job at being intuitive.
Discord is leaps and bounds above all of those, for very different reasons.
About IRC you're obviously wrong :)
Discord is the best thing I’ve found. My group and I love it.