I'm not seeing the reductio in your OP.
Anyway, often fans are just wrong. Often they're making excuses to protect their ego. Oh, Palace weren't really outplayed by Sheffield United, they just had a bad day. Oh, Fleetwood weren't significantly worse than United, they just lack a bit of consistency or that one star player who made the difference that day, we'd have hammered them if we had a player like Sharp.
And since sometimes those kinds of excuses are actually true (see our loss to Villa from the late Snodgrass stunner) it's easy to fall back on them rather than think any deeper. It's like the Leeds away game. Their fans were ranting about how much more of the ball they had, how they had all the chances, but when you looked at the stats you saw they had 0 shots on target, meanwhile we had one that Basham should've scored, one that Basham did score, and one that forced a red card for the keeper. We thoroughly deserved it.
We are where we are because we've consistently bested our opposition over three seasons. Teams often appear to have an "off-day" because we control games so well. Yesterday we doubled up on Zaha and frustrated him to the point he was throwing a tantrum in the first half. They couldn't handle us when we pressed high. They couldn't find a single threatening pass when we sat back. The Palace fans can come up with whatever excuses they want, and they can laugh at me for saying this about a 1-0 scoreline, but yesterday was a very comfortable victory.