I'm not sure if you're being sarcastic, but the parent was offering advice for accessibility to help the member's of the community improve on their projects. Why would you disapprove of that?
So to me the advice makes things worse, not better. 60-80 chars per line???? Even my email is wider than that. Go for at least 200.
This stuff with narrow lines may have been tested on poor readers perhaps? I don't know. All I know is I hate narrow lines - and I especially hate them on websites.
Also, none of those 7 even did a proper A/B/A test on what they claim --while the counter-example is well shown in tons of tests.