Blitting and rendering aren't too different. Blitting is pretty inefficient, too, particularly because many Wayland clients render on the GPU and give you an opaque handle to GPU resources so you don't have to copy pixels at all. And you can blit instead of using OpenGL or if you want, but it's still your job to do so on Wayland whereas on X the X server is doing it for you. You also still need to handle input, focus, multihead, etc all yourself.