Earlier quoted context omitted.
> Below 1700 or so, openings are mostly a waste of time Here is a counter argument - below 1700, someone who knows the strength of an opening would outperform those who do not.
The opening strength will only work when you know how to exploit something small in opponent's opening like a miss of tempo or wrong reply, which I think is above the skill of sub 1700. All the players above 1000 know basic principles like mobility of pieces and developing centre.
That's exactly what I am saying. If one person knows the strength of an opening and the other person don't then the person who knows the opening has a clear advantage. I agree with @skulk's argument though - the time is better spent on learning tactics and analyzing games over learning many opening given the player is sticking to some particular openings.