Second, and where your cluelessness really comes to light, you totally ignore the dependencies. If some other layer – glib, glibc, Mesa, Xorg, etc. – changes something, it can result in misbehavior of higher level software. Distributions that do not ship KDE software as default usually tend to miss that because they concentrate on Gnome or whatever.
Especially rolling release distributions such as Gentoo have next to no QA process. There is a reason why credible Linux distributions have development cycles with version freezes of up to several months.
So to sum it up: There is no KDE mess. There is mostly a dependency mess caused by rolling release distributions that ship new dependency versions without much testing.