> No WM should care about handling raw inputs or forced to be proxy between driver and the app for the output

But.. why? How many WM is feasible to have? Is it really an area where we want a "wide waist"? Should a WM be its own thing? Why not just make it an extension/plugin of a desktop environment, and have only a few of the latter? Being a library call is more efficient and easier to maintain, over maintaining an IPC API (especially that with X, X is just a dumb proxy to the compositor).

> And it shows in complexity and even in power use

You surely mean that X is more complex and has a higher power use, right?