Why do the likes of you raid into threads to start some kind of player warfare? Valencia signs contract, so let's pick on some random, often controversial player in an attempt to look the part. Either way, I'll bite, Kagawa has comprehensively outperformed Valencia over the past two seasons. The first of which Valencia produced quite possibly the worst individual season any player has put in under Ferguson while under the tag 'first team regular'.
He wasn't actually as bad last season, and I don't mind keeping him as a squad player, for what it's worth. I would hope to see the likes of De Gea, Rafael, Smalling, Welbeck and Jones, all of which have two years remaining, sign up soon too.
Your reasoning for his poor form is a bit folly, too. He's been rather wank, primarily because his crossing has been awful and he's struggled when brought onto his inside, at which points he turns back. He really needs to play with more aggression and confidence going forward.