The issue is with lossy scaling. I also have a 4k monitor but you can clearly see a difference in clarity if you select anything other than 3840x2160 (1x, everything is tiny) or 1920x1080 (2x, everything is huge).
But now that it's more widely supported, it's really the more efficient and more precise solution.
I had a Surface Pro 3 with a default 150% scale and the experience in 2014 was great as long as you lived in OneNote.
Many first party programs even still look _awful_ at best, and are non-functional at worst as a result.
In contrast to Mac where your UI draws at 2x and then gets downscaled to fit on screen, unless the user has picked the one resolution option where it's actually native 2x mode, which I never see anyone do because it's not enough space.
I imagine any niche business targeted software on Windows still doesn't do scaling right, but that's the nature of the Windows ecosystem. You can run your software that hasn't had meaningful updates since 1995, and someone will happily keep selling you their software that hasn't had meaningful updates since 1995.