Intel's Tiago Vignatti has a new blog post entitled "the damn small Wayland API." In Tiago's post he points out just how much leaner Wayland is in relation to the aging X11/X.Org Server.
The X11 client API has about 1,278 entry points while Wayland has just about 135 entry points. This is Wayland in its 0.99 release just days prior to Wayland 1.0. Of course, Wayland 1.0 doesn't mark the end of major development and much will be added going forward, but still Wayland is much lighter than the full-blown X stack.