This isn't a complete analysis. High DPI screens are able to render text without aliasing, and that makes a significant difference, especially with less-than-p

This isn't a complete analysis. High DPI screens are able to render text without aliasing, and that makes a significant difference, especially with less-than-perfect eyesight. What you're saying is true insofar as I had to squint up to a 1080p screen at 13" to actually see the pixels. But everything was slightly blurry, and switching to a "Retina" (1600p iirc) screen fixed that. Which was the lack of subpixel aliasing: you can make those screens look blurry as well, by turning it back on. But a 1080 without it just looks like it has janky text rendering. An actual 4K screen is unnecessary at 13", imho, but the extra pixels are harmless except in battery life. I do detect a real difference in textual rendering between 170ppi and 227, because it's the difference between leaning on subpixel aliasing and turning it off while still getting good results.