Could you please explain what you were meaning, why would a low or high resolution be ok for a 27" monitor but a high resolution only be good for a small screen?
Resolution is all about how far you sit from a screen.
Ok -- it took me half an hour to find the link that I wanted to share but I now have it. (I'll save it this time!)
What I meant is simply that Mac OS is designed to look best at about 100-110 pixels-per-inch or at twice that much 200-220 ppi, in 'retina' mode, with perfect pixel doubling. This translates to an 'ideal' resolution of either 1080p (or 4K for retina) for a monitor in the 22" range or else a resolution of 1440p (or 5K for retina). This is the "correct" mode of displaying MacOS, but of course, as you say, one could just sit closer or further from the display. That's a different topic, Apple designs based on what it understands to be typical usage.
As you can see from this chart, a 4K 27" monitor is "wrong", because OS elements appear too small if used natively as 4K, and too large if used as "retina" 1080p (which is what the OS defaults to, by the way). Many people will go into the settings and run a 27" 4K monitor scaled to 1440p because, as most people would tell you, that just "looks" like the right size for Mac OS on a panel that size. But if you do that you are wasting money: you should have just bought a 1440p monitor instead of a 4K.
This is also why Apple never released an iMac 27" 4K, but waited until they could release a 5K 27" iMac, and a 4K 21.5" iMac. Ditto for the LG UltraFine. You will never see Apple officially endorsing a 4K 27" panel because its OS just looks bad on it.
This
link is very helpful, and it contains this great chart, which I think every one shopping for an external display should take note of, and that MacRumors staff should understand before they claim that higher resolution is always better.
I have become convinced that this is an industry problem: they find it easy to manufacture 27" 4K panels right now, so this is what they are pushing. But for Mac users, 22" 4K or 27" 5K are more appropriate.
I personally don't have very strong eyesight (almost wrote iSight there), so maybe I would be content with a 24" 4K and things looking a bit big. But I had a 27" 4K and had to send it back, the OS elements were so big as to be goofy.