I moved from Gnome to KDE around 2 years ago. I just got tired of Gnome extensions breaking all the time, Gnome not being customizable, no support for AppIndicators, etc.

In my opinion, Gnome's UI feels more visually polished than KDE, but that polish doesn't matter when functionality takes a back seat to it.

One extremely minor complaint I have about KDE is that I wish they'd rename "Dolphin" to something like "KFiles".

Yes agreed. It's a very non descriptive name for such a key part of the DE.