Valencia has looked awful at crossing at the world cup too. You can't have a winger who can't cross the ball and isn't one of the best in the world if you want to compete against other teams with players who are.
and as for kagawa, when he plays and especially when he's on a wing he's too ineffective because he's not direct enough. He can't do what the top tip players do like picking up the ball, driving towards the net, beat a player or two and score. Players like messi, ronaldo, robben etc make this look easy but that's why they are so important to their teams and why ronaldo scored a million goals for utd and when he left we lost that drive because neither young nor valencia can do it properly either. Our strikers are too slow to do this so we need other direct players. Kagawa is more likely to trap the ball and play a neat pass. We need that directness. It wins games.