I don't know, I love the way KDE looks and feels. It's very fast and it's quite beautiful. Breeze, to me, is a very aesthetically pleasing theme.
And I'm not just saying that. Since the move to breeze in 5.0 I've thought it was pretty. Since then it's only improved. I really like the icons too - they're vibrant, but not completely flat. I like bright colors, sharp lines, higher contrast.
I really, really don't see this Frankenstein approach viewpoint. To me every KDE app feels and functions like a KDE app. GTK apps stick out like a sore thumb in the desktop world. They have big buttons, nothing is labeled, the title bar is huge for some reason. You kinda just have to guess what clicking buttons does. KDE apps are more closely aligned with traditional desktop applications I've been familiar with since XP. I like that.
On a usability note, I think KDE is super good here too. I really like the apps, many I consider best-in-class.
Kate is really good, dolphin is the best file manager I've used, kdevelop is a fantastic ide. Even random things, like kinfocenter (the system information pop-up) are really, really good. Krunner is great, the new system monitor is the best I've ever used. The new application menu is perfect.