TBH i haven't used KDE Plasma much. I used to like KDE 3.5, then KDE 4 was a disaster that it took several releases after KDE 5 to stabilize (i remember trying KDE Neon, supposedly KDE's very own distro that should be rock solid for KDE - and i had severe visual glitches). But the last versions of KDE 5 and KDE 6 nowadays seems fine. Again, i'm not using it much, i mainly use Window Maker (X11) and use KDE Plasma only on my laptop as well as on my desktop when i want to try something in a more "windows-like" environment or as a different user (for default configurations, etc).

I can believe that KDE Plasma still has issues though, it seems some sort of bomb was thrown during KDE 4 times in the codebase and it still has to recover. Though if nothing else, i do use KDE apps outside of Plasma (Kate, Krita, Dolphin, Okular, Spectacle) and they all seem very solid.

I think Gtk+Gnome and Qt+Kde are being mixed here and it's creating some confusion.

After a parent said that Gnome looked better than Kde I looked it up and found a number of posts criticizing Kde design decisions (padding, etc). I fully believe the Gnome people have a better design decision. But I don't think that criticism applies to Qt itself, necessarily.

It’s not a perfect rule but I find that Qt apps tend to resemble KDE apps and have questionable design choices more often than not, even those that aren’t related to the KDE project in any way.

It’s consistent enough that it makes me wonder if maybe something about the tooling is partially to blame.