Less polished in some areas too, though. It's slowly improving over time but for example fine UI/UX details like whitespace usage, control alignment/placement, and typography have always felt a bit… "off" in KDE as well in most software written with Qt, which I think probably boils down to Qt being more likely to be chosen by devs who are more technically inclined than design or UX inclined.
In my opinion GNOME and GTK apps generally get those details more "correct", though GNOME 3 and up goes way overboard on padding. Strip that padding down with a theme and its design is solid though, and Cinnamon, XFCE, and MATE get these right out of the box with no modifications necessary.
But that's why these "X has a better UI than Y" arguments are silly. I prefer KDE to any other DE because it worked (I now use MacOS and can't run other DEs) for me, and most people who prefer other DEs. That's OK. They all have different strengths and weaknesses (customization, resource usage, ability to run on certain OSes, high DPI support, etc).
In my opinion GNOME and GTK apps generally get those details more "correct", though GNOME 3 and up goes way overboard on padding. Strip that padding down with a theme and its design is solid though, and Cinnamon, XFCE, and MATE get these right out of the box with no modifications necessary.