X is a dated mess at this point. Its core architecture assumes a model for drawing graphics that is more than teo decades out of date. There have been extensions - plenty of them - to drag it along and these have added substantial bloat. Also, some extensions where also awfully half-baked, turning the X11 protocol into nightmare to program against.

Wayland has some good ideas to modernize the stack based on passing GPU buffers between the compositor and applications, so that applications can use GPU acceleration and actual 21st century graphics technology to the fullest. But the non-graphics part of a desktop GUI are hard (e.g. event routing, clipboard, drag and drop, screenshots/capturing...). Wayland suffers from two things in this regard: first, it needs to catch up to a 30 year headstart thatball other DEs have with implememting that. Second, it is artificially hobbling itself by declaring absolutely trivial information privileged like the screen resolution and absolute coordinates of any window on the screen. This is a list of stumbling blocks and showstoppers that have to be worked around.

Because X's developers gave up on it: https://www.phoronix.com/scan.php?page=article&item=x_waylan...