That's why I mentioned he isn't an automatic starter, he's done well, nothing amazing but personally I'd rather push Rooney up top, drop rvp/Falcao and play Herrera alongside Carrick, blind, Di maria and mata with fellaini rotating in. Just a normal 4-2-3-1 basically. All those players have shown a lot more then the strikers who don't really fit in at the moment. Never going to happen though.
Anyways, its not like all the midfielders have been consistently brilliant or even fit. They've all been more or less at the same level so its not so easy to pinpoint the best performer. I definitely understand why he isn't starting all the time, I just don't agree when people say he's been poor or not good enough to start. He's done well, just so have others that he's competing with for the most part.