It's not like only one midfielder's allowed to pass the ball really well though.
Carrick's a terrific passer. He's not as good as Scholes at his peak, no, but he's bloody good. For years he showed that to an extent, but he also deferred to Scholes massively. Countless times I've seen him give it square to Scholes five yards away under no pressure - in a position where Scholes would never ever have given it to him. That gets the ball to our best passer, sure, but it has a cost in terms of the speed and fluidity of our play. It would probably have been better, overall, for him to show some balls and play more of those fantastic passes to the forwards taking the opposing midfield out the game.
It's probably true that you can't have two CMs equally dominant. But he could have been much more dominant than he has been. He's spent the best years of his career... not water-carrying, that's too harsh... but facilitating others rather than playing to his potential.