Lines or code is an indicator, not a goal. If you write long-winded functions, your code is bug prone and harder to test and verify. If you refactor it, it gets shorter. Where do you draw the line?
The same goes for how many characters you accept between two line breaks. Some go for 76. Some for 130 or more. There is no difference if your line has 129 or 131 chatacters, but if you spew a comment with 999 characters in a single line then your feedback is actionable if you say "hey man, don't be that guy. Rewrite your comment and make it readable."
> (...) PR reviews would be better by actually judging things like readability directly rather than relying on measures that estimate those qualities.
Not really. Calling out basic things like "this function is far too long" is clear, objective, and actionable feedback. That is a good PR comment.
Dismissing clear and actionable feedback as some guys whims is a red flag, and a telltale sign of someone who has no interest to improve their output and address issues.