I think you are underestimating how much influence a manager, and their tactics, have on a game.
It is not just a case of a manager sending 11 players out there and saying, go on lads, get on with it.
Winning a game will often be because of who you pick, your formation, your tactics, who marks who, the players motivation and so.
Just stopping Barcelona scoring a goal is some feat
Yes you need some luck, but if any managers team beats Barcelona they have a right to "crow" about it.
Look at Yeovil v Birmingham on Saturday in the FA Cup. Yeovil went 2-0 up then the Birmingham manager made some changes, got the players to push up harder on Yeovil, and they won 3-2.
Without the managers changes to formation and tactics they probably would not have won.
So the Birmingham manager has a right to crow.
If it is was JUST down to the players then the team with the better players would always win, but the manager has a huge influence, look how good Fergie was for all those years, that was not luck.