I will acknowledge that the user whose comments I am complaining about is higher-rep than I am, and thus presumably more helpful and respected. Nevertheless, I have repeatedly seen categorical statements which I know, from direct and personal (admittedly anecdotal) experience are wrong, and often misleadingly so. Other than repeatedly correcting said user, what can be done to ensure that learners, at whom this stack is aimed, are not misled about English, whether formal or idiomatic? The question that I feel was the "final straw" is this one, regarding translating a Czech idiom into an equivalent English idiom, but this is far from the only one where I have encountered similar incorrect and categorical statements from this user.
If it's in an answer, you can downvote the answer, and/or leave a comment.
If it's in a comment, you can flag the comment, and/or leave a constructive counterexample (as you did in this case). If someone else has left a comment, and you share that sentiment, upvote that comment (as I did in this case).
Incidentally, I've made a few erroneous comments myself on ELL. Rep points don't necessarily make us more respected, and people with more rep aren't less fallible.
As a footnote, I agree wholeheartedly with your assessment about categorical statements. It's one thing to say, "I've never heard this phrase before," or, "I don't think I'd be inclined to word it that way," or, "this word is not too common." It's another to say, "This means nothing in English," or, "This form of the word is never used." It's very frustrating to see such unequivocal statements tossed around, especially when they are clearly erroneous.
I think some of these "incorrect categorical statements" are simply due to simple misunderstandings and faulty assumptions. One good example of this can be found here, where a user commented:
In other words, no present after because.
I agree: terse comments like that one appear to be categorical; however, when the user who made it was called out, a clarification was made:
You cannot possibly think I mean in all cases?
(Well, actually, the comment sure reads like someone meant, "in all cases". But at least that got cleared up.)
We all need to be learners here. When a member insists that something is "never used" or "means nothing," it would be nice if some well-researched counterexamples might prompt that individual to soften their language a little bit, using words like seldom instead of never. Unfortunately, some of us are slower to learn than others.
One more thing: If "win by a nose" doesn't mean anything in English, then that goes against the fruits of my research; I wonder what these authors and journalists were talking about when they said:
Quebec Solidaire won by a nose, with 30.6 per cent of the votes; the Liberals' Anna Klisko had 30.3 (with a margin of fewer than 100 votes)
Heller only won by a nose in 2012 – and the health care debacle makes this state the most likely to flip next year
That year's (disputed) presidential election was won by a nose by Fox's successor, Felipe Calderon
If he is considering two job candidates and the only thing that differentiates them is an internship, that person will win "by a nose"