Maybe that's because my eyesight is not that good lately. Even considering that, I really can perceive a 150% scaling on a 4K monitor when I see it. It isn't that bad and sure you can work with that, but man, do try 5K at 200% and then tell me about it.
It's a real tragedy there are not more 5K displays. The Apple Studio Display is expensive and a little absurd with that webcam and the A13 chip, but at least you can enjoy that resolution. I wonder if display makers will consider this someday and stop selling so much gaming models and so little 'work' models.
Therefore it makes sense to buy either low-dpi monitors (with dpi ~100) or high-dpi monitors (with dpi ~200, and run it with scale 2), but 28" 4k is just in uncanny valley of dpi, that is too high for scale 1, too low for scale 2 and matching scale 1.5 is blurry.