The UI is the easiest thing to fix and as you have shown already has been for some time. What separates IRC and the rest is all the features you would expect by default in a messenger of the 21st century:
- history
- with search
- logins
- simple bots
- automatic content fetching (wiki/youtube Links, pics and gifs)
- file transfers that just work
- image pasting
- message editing
And probably others. Yes, those features exist in one way or another in IRC. The point is not whether you can or not; the point is how much time and energy do I want to spend to install and maintain those. I may have had the patience to do it a few years back, but I value other things now.