KDE nowadays is buggy as hell and quite a lot overrated as a desktop environment, it has bugs everywhere in its main components: Plasma, Dolphin, Kwin. And that's just the X11 version.

The Wayland Plasma thing isn't really as mature software as you could say about Gnome and other Wayland software.

Somewhere in the dev community behind KDE most devs are chasing shinny new things and apparently won't botter to debug spagetti legacy code (the stuff behind 80% of the desktop environment), so serious bugs are a daily thing, even more after upgrades, because of regressions everywhere.

KDE 5.xx (and probably 6.xx, because it is mostly 5.xx code), IMHO is quite now on pair with the infamous version 4 (buggy as hell as well).

The "easy no memory" thing isn't quite right neither, IF the apps, components, whatever run without bugs - unlikely, even for common use cases - that will happen, but more often than not, you'll find your CPU/RAM in really bad shape because some misterious thing - KDE component, library, even the window manager itself - it just has failed somehow.

Or maybe your KDE just freezes over, out of the blue, because no good reason, Plasma could just dissappear in the middle of a rutine desktop task (closing/opening a video, taking a look at the preview window in the panel, etc.).

so, you could take this words as a rant, their not. They're just experience of maybe the last two, three years with KDE. And boy, lots of users could write the very same things.