You're by and large right about this. But the one area that it isn't true is offside. This is what it says in the laws of the game:
player in an offside position at the moment the ball is played or touched* by a team-mate is only penalised on becoming involved in active play by:
- interfering with play by playing or touching a ball passed or touched by a team-mate or
- interfering with an opponent by:
- preventing an opponent from playing or being able to play the ball by clearly obstructing the opponent’s line of vision or
- challenging an opponent for the ball or
- clearly attempting to play a ball which is close when this action impacts on an opponent or
- making an obvious action which clearly impacts on the ability of an opponent to play the ball
There's no grey area there at all. And I challenge anyone to tell me that Gylfi clearly did any of the things that make someone offside without touching the ball. Clearly obstructing the line of vision? Nope. De Gea saw it the entire way. Challenging an opponent? Nope. Attempting to play the ball? He's literally done the opposite. He tried to not play it. Making an obvious action? I fail to see how moving his feet toward his body is an obvious enough hindrance to anyone.
It's just such a ridiculous decision. Unfortunately my memory isn't strong enough to remember another one where a player was similarly positioned and it was let stand, but I've definitely seen it. They've chosen in a huge moment to make a call that is never made and is not in the spirit of the rules, if even within them at all, and of course it goes against us.
I'm still fuming if you can't tell.