Unfortunately, what I found was once you added plugins and themes and this and that, there was too many breaking changes when considering the whole UI system. This is not really a technical fault of KDE devs themselves, but it turned into something akin to managing a node.js project. Yes I know it you use less plugins it's better, but I want both: plugins as well as pixel perfect consistency.
I found similar issues in gnome, where it's even worse since the DE itself pushes tons of breaking changes. Note that I consider even a settings menu reorg as a breaking change.
I finally settled on XFCE, where for years now, nothing has changed. Not even one pixel. The menus are the same, the search results come in the same order so I have muscle memory like "<text> arrowkey arrowkey enter".
That's my expectation from a DE. I basically have the entire desktop byheart. And this culture seems to extend to the plugins as well, for example the various xfce4-panel plugins I use have all been pixel-perfect equal for years now. My themes and what not have never broken on me either.
Windows up until 10 also had similar properties, I had a crap ton of plugins with rainmeter, 10k+ LOC AHK scripts, etc, and nothing ever broke.
I also like that the shared library disease isn't that high in XFCE-land, in KDE installing something needed too many common k-* packages. I understand KDE gives a whole suite of apps so it might be necessary, but this also meant that I cannot use KDE apps even the ones I liked, on another DE without also getting... kwallet or something iirc.
The thing I miss the most from KDE is wobbly windows. I would kill for that feature, but unfortunately, I don't think I would tolerate breaking changes for that feature.