Wayland isn't bad design, at least not in the way you're describing it. I feel like there's some confusion about what Wayland actually is. It's a document that describes how surfaces ("windows") should talk to a compositor ("display sever"). That's it. In a parallel universe Kwin and Mutter would be X11 display servers and we would have all the same issues. Nothing is stopping the existence of a single extensible compositor to rule them all and be the base on which every DE/WM is based but it hasn't happened yet.

When people talk about "pushing stuff to the DE" what they mean is the Wayland project aggressively scoping the Wayland protocol to drawing surfaces and handling input events. They're not trying to become a generic desktop message bus for everything an application might want to do -- that's literally what dbus is.