Funy that you mention multi-monitor since it's one of the reasons I eventually moved to Wayland. The only way to support different DPI monitors in X was to do janky scaling or even jankier multiple X servers.

I don't use KDE (or GNOME anymore) but while I had to deal with a lot of initial speedbumps a couple years ago, these days instead of a full DE, I'm using a Niri setup and it's worked out great for me.

For my laptop, I have my own monitor-detection/wl-mirror script for example that is faster and more reliable for plugging into projectors/meeting room HDMI than even my old Macs.