Wow, shocked that Gardner has so many issues with KDE, especially as I think differences between DE's these days is approaching "tyranny of small differences" territory. You can make almost all of them function like the other - except Gnome. I used to run Gnome and KDE side-by-side, and it took 15 Gnome extensions for me to emulate the functionality of KDE OOTB. Also, many of the 15 indie developed extensions would break every time Gnome updated, and I would hope and pray that the devs would eventually repair them. Add to that the performance hit of all those extensions. Gnome would end up using much more memory. And that painful frame rate on, well, everything. Even Windows 10 looks like it renders like silk compared to Gnome. And I don't know if it was the famous Gnome memory leak or something else, but even with oodles of memory to spare, after running more than 3-4 productivity apps simultaneously would start to lag the system badly, while KDE under similar loads would feel no different than if nothing were running.
I'll be the first to admit that the KDE UI (especially panel config) has a leaning curve, but they're making good strides there. KDE is just so fast, so smooth, so configurable, so refined, and so powerful that I can't see using anything else as my daily driver. Add Plank dock and Ulauncher and it's perfect.
My #2, BTW, is Budgie, which is also super fast and smooth, and the Ubuntu Budgie team has developed terrific applets. It's really what Gnome should be. I'm also really enjoying Deepin as well, although it definitely needs some FPS and hot corner refinements. All of these, BTW, on Manjaro.