Wayland is better for gaming. It has a noticeably lower latency because the entire Wayland stack is implemented in a single program (what they call the compositor) as opposed to several in the X11 stack (X server, compositor, window manager) that need to communicate with each other.
Games under X11 use DRI just like with Wayland. Beyond “create a window and handle resize events” they don’t really interact with X11 or your window manager.
We should expect similar performance and indeed that’s what we find: