it falls to each and every individual app to (re)implement everything: accessibility, clipboard, keyboard, mouse, compositing etc. etc.

I haven’t read so much nonsense packed in a single sentence in a while. No, apps don’t implement any of these things themselves. How the fuck would apps simultaneously “implement compositing themselves” and also neither have access to the “framebuffer” (which isn’t even the case on Xorg!) nor information about other windows on the screen?

Please, don’t rant about things you clearly don’t know anything about.