No wonder you had a poor experience. Distros that don't treat KDE as a first-class DE are well-known to have a generally poor KDE experience. Kubuntu is probably the worst KDE-focused distro, and you didn't even start with Kubuntu as a base.
A slightly poorer experience for a distro's non-flagship DE is one thing, a major binary being outright missing is another. This should have still worked - Ubuntu does support adding KDE by installing that package, kubuntu-desktop depends on plasma-workspace which contains /usr/bin/ksplashqml.
