This game is the nail in the coffin.
With Valencia and Young it's just suicidal. Can't win a game playing 3-5-2 with utterly worthless wing backs, in an attacking sense.
Valencia especially is just too thick to play in this sort of system. You can see he hasn't got a clue where he should be and thats before you even get to his walking-pace movement on the ball and shambolic crossing.
It's also getting the worst out of Mata, rather than allowing him to play at his best. He needs players moving around him whereas right now all he has are two static targets, because the wing backs are never where they should be and, Di Maria aside, the midfielders aren't getting up alongside him.