>> Using a compositor fixes screen tearing, no need to use Wayland for that.

Right, and that abandons the whole X drawing API in favor of passing around client drawn bitmaps. That was one of the big points of Wayland too - X has a whole bunch of stuff that no modern apps use anyway so lets throw it out and build up a better version of the capabilities we need.

If we abandon the X drawing API and half an OS included (memory management) and use KMS, all that's left is the features that are security holes.