You're supposed to use KDE with Xorg if you want things to just work. KDE with Wayland if you're adventurous.

Therefore newcomers should use Kubuntu or the likes of it

KWin/Xorg AFAIK has been on maintanence duty (i.e. fixes mostly come from XWayland) for >5 years now. KDE has expulsed the Xorg codebase of KWin into a seperate repo in preparation of a Wayland only future.

Even if KDE/Xorg is a stable experience is true now, it will not be true in the medium to short term. And a distro like Kubuntu might be 2 years out from merging a "perfect" KDE Plasma experience if it arrived right now.