The post that was quoted here has been removed
You're quite right, but I think your last point is only true if the player still wants to, and believes himself able to, advance as a player. At the club level, there are a lot of players who know who and what they are, are settled and content in their position on the board, and play chess just as an amusement. I certainly see that at my club, at various levels.
And if that level is "about as bad as Shallow Blue's", well... against my usual opponents it pays to have a system you know well and your opponent doesn't, even if it's not the best. Too many of them play boring, stodgy openings which my superiors will smash through with no problem but which I struggle to get a handle on. On the flip side, they never walk right over me, either. It's always "who makes the first blunder in the boring middle game".
I myself can't be bothered with that. I try to play proper book openings. I have no delusions that I might grow into a good player - too old for that by a few decades - but at least it gives me a chance to make interesting notes. I can't be doing with a closed four knights'. Frankly, I prefer losing to our club champion in what is at least guaranteed (we both know this!) to be a proper, open Sicilian.
Mind, they're not always boring. Some of them know their niche, as well, but it's an agressive one. One of these guys always plays the Bird. He has great success with it, too, because he at least loves attacking the kingside, is genuinely good at
that, and his opponents have no idea how to handle it. Until I booked up just a little and served him a From... that was fun.
But no, in general, at the level these guys are playing at (i.e., mine), and with the attitude they play with (
not mine!), time invested in learning pawn structures would be wasted. None of it would stick, that's not the level their mind works at. They're woodpushers, as am I, and unlike me, they have no delusions of being a frustrated IM.