As a decades-long Xfce user, I greatly value Xfce's modularity, and don't care the slightest bit about improving the display server performance. Xfce is already snappy well beyond my level of sensitivity, and I won't trade the flexibility I have and use for a sliver of extra performance I don't even think I might need.
(Yes, it's plenty snappy on an external 4K@60 monitor. A desktop environment is not a competitive FPS where a single extra frame of latency lowers your chance of being productive.)
It's a specific setting in XFCE you have to turn on, and most people try to bypass it anyway by manually disabling the compositor with hotkeys. Auto detection of the full screen windows has been hit or miss, especially when running things through proton/wine.
Also with x11 if you go through the steps to get Variable Refresh Rate going and you are dual monitor, it will max the refresh of both to the slowest monitor. :(
These are valid concerns for those who spend more time playing maybe. I mostly work, all of my monitors are 60Hz, and I only play single-player games.
If I were into hardcore gaming, and used the same machine for daily work, I would likely just end the X session, and switched to a minimalist Wayland session with a menu of games for the entire desktop.
(Yes, it's plenty snappy on an external 4K@60 monitor. A desktop environment is not a competitive FPS where a single extra frame of latency lowers your chance of being productive.)