OS X not only uses a lame hack to scale, it completely muddles the issue by introducing the concept of "HiDPI" UI elements. Somehow I can set my 4K monitor to use "native resolution" at 3840 x 2160, and yet the UI and fonts look fuzzy! Absolutely terrible, and a complete embarrassment for Apple imo since they are supposedly the UI kings. You only don't notice the issue because you're using a 27" 5k display, which has been "blessed" by Apple as the "correct" DPI to match native screens. For those of us with 4k screens (95% of the market), I guess we're just supposed to enjoy a subpar experience. Even X11 looks better.
For me, I only closed the book on the issue after finding BetterDisplay [0]. Basically a 3rd party program that gives you complete control over resolution, display density, and a ton of other options on MacOS. It has a trial mode but it is well well worth the money. With that + the CLI tweak to set font smoothing to 0, the 4K experience on MacOS looks decent. You can even decrease the effective scale of the native screen past "More Space", so those of us with good eyes can actually take advantage of the screen real estate.
Also, if you're curious to explore this issue beyond my subjective thoughts here, these [1] [2] blog posts do a great job diving into what is so bad about MacOS scaling, why 4K 27" or 32" screens end up looking bad, and why 5K 27" look okay.
For me, I only closed the book on the issue after finding BetterDisplay [0]. Basically a 3rd party program that gives you complete control over resolution, display density, and a ton of other options on MacOS. It has a trial mode but it is well well worth the money. With that + the CLI tweak to set font smoothing to 0, the 4K experience on MacOS looks decent. You can even decrease the effective scale of the native screen past "More Space", so those of us with good eyes can actually take advantage of the screen real estate.
Also, if you're curious to explore this issue beyond my subjective thoughts here, these [1] [2] blog posts do a great job diving into what is so bad about MacOS scaling, why 4K 27" or 32" screens end up looking bad, and why 5K 27" look okay.
[0] https://github.com/waydabber/BetterDisplay
[1] https://bjango.com/articles/macexternaldisplays/
[2] https://bjango.com/articles/macexternaldisplays2/