Truth be told, I don't care much about the aesthetics per se -- with the exception of the dark theme, that has to be the best thing to introduce in a while!
Windows UI has deficiencies, all Linux WMs have some deficiencies (although some are unbelievably customizable and I like them), macOS is no exception as well. I don't care. I want it to work stably, predictably and be somewhat pretty. macOS ticks the boxes. Windows used to but it's very idiosyncratic lately. And the OS is just somewhat slow even on a very beefy PC where games can't go below 120 FPS... and your OS still manages to lag. Not cool.
In any case, I am not under the illusion that the iMac Pro + macOS will be the "perfect" machine and OS. Not at all. But between getting tired of tinkering with minor crap, UX inconsistency, lags and software compatibility to me the Apple ecosystem is the best compromise. Not trying to convince anyone though, simply explaining my thought process that led me to my decision.
But I agree Windows is descending -- they fired the guy the righted the ship and made Windows 7.
For Apple, it's always hard to be sure anyone their really cares about OS X and professional hardware.