Not for me. I switched to Kubuntu in 18.04 LTS (after many years of OpenSUSE, so I've got a pretty good idea of how a polished KDE distro looks.) No complaints at all. Kubuntu use to be a poor rendition of KDE but it's working great now.

I'm pretty happy with Ubuntu generally; kernel-hwe is outstanding. With 18.04 LTS you still get updated kernels; it was released with 4.15 but with "hardware enablement" updates it's up to 5.3 now.