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.

not exactly if the person can't use the slight advantage for their benefit. They only have window of 2-3 moves at max to exploit less developed pieces else the advantage fades away(assuming non point positional advantage). It is hard for 1700s to exploit very minor advantage and most of the time the win is due to a blunder by opponent.

1700 rating is not very clearly defined since different Chess websites uses different ranking system and the rating can vary dramatically. For example, on average there are 400 points difference between chess.com and lichess.com ranking.