The real issue with Wayland and “setting back” isn't what the article says, but just that like 15 years was taken just to get Wayland on semi-decent feature-parity with X11 during which time development on X11 came to a standstill. That time could've been used to improve X11 and it's still not real feature parity.
And part of it was just the devs refusing to believe that people needed those features. I talked with them around 2010-ish and about some of the things they cut out claiming that no one ever used them. These were things related to mouse acceleration that is pretty essential to video games and image editing, certain forms of screen capture, various things with fonts and color management that are essential to many professionals and they actually believed that no one used those things. Eventually they came around and added many of those things back in, in doing so basically making many of the initial security promises complete void again but so much time has been put in what isn't much of an improvement to justify the time spent on it.