That's actually pretty objective, long lines force you to move your neck and your eyes more which is more straining. I rarely read HN comments on my laptop because of the unreasonable line width, it feels much more comfortable to read on my phone

You're literally describing your own subjective experience. I can move my eyes all the way to each side of my screen with my neck stationary, and I don't feel strained. "Subjective" doesn't mean I'm saying you're wrong about your experience; I'm saying you're wrong about my experience, which you are.