Even considering a resolution below 4k on a large monitor is absurd. This invalidated the whole article for me.
UI scaling set to have enough space and font size for readability.
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.
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.
(Edit: I’m using macOS, might be different for other systems)
For all the folks confused why I'm saying you don't want a 27" 4k monitor for text, it's because the PPI isn't nicely sized for 1x or 2x, which means you have to set it to scaling that rounds and blurs subpixels.
More info: https://www.caseyliss.com/2017/5/17/retina-monitors
By the way, I'm sure most 27" 4k monitors look fantastic and you should enjoy them! Especially if you don't mind or notice the scaling rounding or if you run it @2x and like the 1080p real estate.
This appears to be either a misunderstanding or a description of a deficiency in your environment for example Apple devices. For text there are 2 factors that control its size the designated size in points and for apps not sophisticated enough to scale elements appropriately according to DPI a scaling factor.
You appear to be suggesting that if you only had one knob you would be stuck with text that was either too small or too big however one or an application can adjust the size of the text independent of an integer scaling factor to produce a desirable end result. The same thing is true of images which are already trivially displayed at a different absolute sizes like every image on your browser ever.
For example on Linux most apps you are liable to run that aren't simplistic text apps are liable to be either QT or GTK. QT apps intelligently scale, GTK apps rely on a scaling factor one can set for example with an environmental variable. In both cases there is a setting for font size that effects 90% of apps of that stripe the minority having their own configuration.
It is incredibly trivial to have an environment that looks nice at any size.