I think nitpicks are a problem on LW, not because they clog the comments, but because the expectation of them can disincentivize some new people from posting at all; if more people like a nitpick than the OP, then the person who posted the OP can feel like a failure.
ISTM the issue would be neatly solved by the thing people keep proposing, different axes for agreement and importance. If you get more actual credit and visibility for making an important point than for making an absolutely correct nitpick, behavior will shift.
I think nitpicks are a problem on LW, not because they clog the comments, but because the expectation of them can disincentivize some new people from posting at all; if more people like a nitpick than the OP, then the person who posted the OP can feel like a failure.
ISTM the issue would be neatly solved by the thing people keep proposing, different axes for agreement and importance. If you get more actual credit and visibility for making an important point than for making an absolutely correct nitpick, behavior will shift.