Possibly the reason is because AMD's Linux driver is Wayland compatible, while Nvidia's garbage driver effectively isn't. Wayland will run ever so slightly faster than X11, because it's a more optimised pipeline (X11 was designed back when UNIX systems generally consisted of multiple clients connecting to a central minicomputer, so the idea was the server could run on the weak microcomputer client, while the application displaying a window would run on the much more capable minicomputer). Wayland is more Windows-like in that it doesn't bother with the client-server model. Slightly better performance, but you lose utility features like being able to remotely run graphical applications with ssh -X.