It's still a bit relevant for CJK, but not as much as it used to be. CJK have some really complex charactrt that hidpi@2 still isn't enough to present perfectly. For example `國` has almost 6 horizontal line from top to bottom. If you are in dpi@2 and set font size to 10. You need to present a correct line with same width within 3 pixels. Which isn't that 'enough'. Although the information density of CJK character is high enough that it is readable even it is somehow blurry. It is not a good reading experience.

And what about non-hidpi screen? I don't even know why people are about to read small text of such complex character without sub-pixel anti-alias.

And this is precisely what frustrates me about Macs and their focus on Retina displays: historically horrific support for the world of external monitors. It does not even shock me when Apple rolls out a laptop that only officially supports a single secondary display. This is only further complicated with the only 'Canonical' external displays offered are either woefully out of production or charge as much as the laptop itself just for the stand.

And say what you will about ClearType: at least you can turn it off. I recall trying so hard to do the same for my Mac only to find out my instructions, including massive config changes, sadly no longer worked due to a version bump of the OS.

Subpixel antialiasing also looks weird with scaled video modes (where the screen is rendered at a higher resolution then resampled at the native resolution), can't really work correctly with translucent/transparent backgrounds, and can look weird when mirroring or dragging windows between displays with different subpixel order.

The vast majority of external screens in existence are lower than 150dpi. Most high-end/high refresh rate screens are similar.

yes and that's because the relevant value IMHO is not resolution but DPI. A large 32" screen is bound to have relatively low DPI even at 4k, compared to smaller screens

You need a better monitor.