I use KDE and have for 10+ years. In my experience, kwin is the most stable and performant it's ever been. I don't notice anything at all, ever. Under X, it was common to get stuttering, tears, and dropped frames. Not anymore. I mean I run 2 204hz 1440p monitors. And it's perfect, always.

I'm not saying you're wrong, but it's clear that basics of window management are not universally broken under Wayland. It works well for me and has for a couple of years.