The difference could be much larger on a slower monitor. However the differences between Wayland and X11 as protocols is negligible. XWayland as an implementation looks to have a limitation.
And the non-xwayland numbers are all within a single ms of each other.
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Not to undermine the measurements of the author (agree with you, it's a cool effort), but my read is that this was basically proof that it doesn't matter.
The saying we have in bike racing marginal gains is "leave no stone unturned, but turn over the big ones first"
So sure, first make sure your internet connection is solid. Then make sure your hardware and game settings are optimizing FPS to a reasonable point of diminishing returns.
Then make sure you don't use XWayland
The visual latency on gaming could be different but I suspect not, I think it is more an issue that some people fixate on the latency, others just accept and adapt to it. Games do have more possible sources of latency, visual, audio and io, and if these can all be different that can be difficult; years ago I had an issue with this and midi, that one really threw me off. Games may also not model the physics of sound? does sound travel slower than light in games? That could worsen the problem since sound does travel slower in real life and we are used to that, we expect it.
Consider also that people neither run the latest thing nor the fastest software and remember potholes long after they are filled. EG it wasn't that long ago that wine was running on xwayland almost exclusively for instance and the majority of popular titles run via wine.
I've been a fan of Hyprland for gaming so far. Much more configurable for things like VRR/tearing and other precise tweaks via Gamescope than when I was on AwesomeWM with X11. Been especially nice having Lua for configuration, which finally feels very familiar with my AwesomeWM roots.
I have very fast internet on both sides, both fiber to the home, with only the tablet running moonlight being on WiFi.