And some design decisions are.... iffy at best. Like the fact now every DM have to implement its own mouse(trackpad etc.) management coz "well we don't wanna" (basically, I'm sure Wayland developers have better articulated response to why everyone else involved have to duplicate the code).
Or how many hoops software have to jump just to record screen (or is that fixed now?)
I think the biggest mistake of Wayland was the rush on early migration for general use before it really had time to soak. The general design and not having everything in the display server itself is perfectly fine.
In the case of Vulkan its: I interact with the graphics processor, and don't care if you have a display so windowing is an extension and has platform implementations if applicable. And in the case of Wayland its: I am a protocol for managing and displaying windows, and I don't care what kinda inputs you have (example: VR doesn't have classical PC inputs).