Actually no, i am also under the same suspicion. The thing is that in this 4-4-2 (or 4-4-1-1) with the two holding midfielders we rely heavily on the wings to build up our attacking plays and get the ball forward. Which means that our wingers must spend a lot of time in the middle third of the pitch, effectively hold onto the ball under pressure, provide defensive contribution and of course carry the ball forward.
This is what made Young "irreplaceable" in the first place despite his lack of qualilty, his overall contribution. Last Saturday i almost felt sorry for Mata when i was watching him running up and down the right flank and trying to make himself useful. Against a more creative FB we would probably have more problems.
On the other hand, both Mata and Pedro flourish when they're given the opportunity to stay in the final third. Tracking back full backs and contributing on both ends of the pitch isn't really their cup of tea. You can't have four players who can only contribute in the attacking third (Rooney, Memphis, Pedro and Mata), it's too risky. Even Barca has three.
Pedro is stronger than Mata and he can offer much more in our pressing game. But the main difference is that Pedro will pass the ball and then look for a run in the box, behind the defense and he will try to beat his marker when Mata will pass and look for the next open space in the midfield to occupy. Pedro's better at making things happen in tight spaces than Mata.
In the best case scenario we'll hopefully see a return to last season's 4-3-3 with Carrick-Schweinsteiger sharing the holding role, Morgan and Herrera as the two b2b midfielders (a more fit Bastian could also play there) and Pedro-Rooney-Memphis up front and Mata being the first to come on whenever we want to try something different.