Definitely, and it's probably not very noticeable, but there's no escaping the physical problem of not a perfect 1:1 or 2:1 pixel ratio.
Say you have a UI element that's supposed to be 9px wide. If you have perfect 2:1 pixel ratio you can use 18 physical pixels and it's as sharp as the monitor can be. If you're using UI scaling of say 1.5, the monitor needs to use 13.5 physical pixels to render it. Except that's not possible, so it will average together the 13th pixel with the 15th pixel (simplifying). It's basically introducing an extra anti-aliasing pass to your frame. This is is why the Apple/LG 24" is 4k and the 27" is 5k. All that said, I'm sure 4k @ 27" even with 1.5x scaling still looks great and you'd never notice the difference, except if you had the two right next to each other.
Yea it's good enough. I'm using a 27" 4k with my Mac, scaled show the same amount of stuff as a 5k would, so 125% I guess. Sure it probably looks worse than a real 5k monitor if I was to pixel peep, but it's great to me and I don't think 5k is worth the more than 2x asking price.
Scaled resolutions work much better than they used to. For example the iPhone 12 Mini scales at 2.88x by default and I've never heard anyone complain.
However I think it might also depend on the specific panel. I have a Lenovo portable monitor which is 1080p at 14", and running it at anything except 1x looks absolutely awful.
