Last I checked getting a 4K monitor to work under linux was a very involved series of configurations. My current MacBook has a retina display and effortlessly supports a 4K monitor as secondary screen. Retina alone is a game changer.
Combined with better text anti-aliasing it makes macOS by far the most pleasing/productive experience for development I've ever used (disclaimer: I have over a decade of experience in both Windows/Linux desktops.)
I stopped believing in desktop on linux a few years ago (and I really wanted it to work!) Things are getting more fragmented instead of unified; that adds lots of extra work for users and app developers, which result in a frustrating experience and vastly different UIs depending on versions/toolkits used. I don't think a commercial desktop will change any of that, even a fully dedicated and financed team will take years to barely get on-par with the desktop on macOS.
There seem to be a lot of misconceptions about the whole developer's environment thing. "Made by developers, for developers" and "all that money for such a closed box" sound a lot more like wishful idealism than actual "best tool for the job" pragmatism.
I also used to think linux was the best desktop, and did so for a long time, because of "by developers for developers, open-source" and other righteous sounding things. But believing you're using the best tools and actually doing so are two different things; I wasn't even living in Emacs or aware of how superior the VIM language is back then, so much for using the best tools ;)
Its easy to fool yourself into thinking you have the best tools, and its near impossible to tell you actually do.