> Is it a Wayland vs. X11 thing?

Yes, most likely. Without a compositor I get lots of stuttering on x11, whereas KDE and GNOME's wayland sessions are both buttery smooth out of the box.

Might be my Nvidia GPU, but I've never gotten x11 to work flawlessly for gaming.

> Without a compositor I get lots of stuttering on x11... Might be my Nvidia GPU, but I've never gotten x11 to work flawlessly for gaming.

Weird. I don't use KDE's compositor, and -AFAIK- WindowMaker doesn't have one. When in either KDE or in WindowMaker I don't have stuttering with either fullscreen, borderless "fullscreen", or windowed games... everything is as smooth as it is in Windows. Having said that, I do know that -when using KDE- some fullscreen games get jittery as all shit if a notification pops up and remain that way until the notification disappears. I expect that that performance problem would go away if I was using the compositor... but I don't want to spend the VRAM on it.

I use AMD graphics cards, so it might be an Nvidia thing that you're seeing. It also might be a "Your Linux distro simply stopped shipping good xorg installs" thing. I'm running Gentoo Linux which continues to ship updated versions of xorg and supporting software. [0]

[0] I've heard people running Debian and Debian-derived distros report X11 behavior that absolutely does not match what I've been seeing for years... so some percentage of the "X11 can't do $THING" when it really, really can must be coming from distros that ship either dramatically out-of-date or severely crippled xorg installs.