No it's just lazy criticism by people who can't see the wood for the trees.
Here are three heat maps that prove the argument is an outright lie.
First, the heat map of United under Moyes. Look at the concentration of heat on the right wing, the right winger has been getting chalk on his boots, staying as wide as possible and stretching the play.
Now compare it to Mata's heat map from the Fulham game. Notice that whilst he is nominally starting from the right, the heat signature shows him drifting in and in and in. There is less attempt to get beyond the left back and into a 'wingers posistion' behind the full back as there is to come back into midfield and play the ball.
Now compare this to Mesut Özil who no one is stupid enough to make the argument is playing 'wide right', notice the large concentration of heat, throughout the season, in almost the exact same areas that Mata operated in against Fulham.
And this is in a team whose primary tactic was to get the ball wide and cross it yet Juan Mata, nominally playing from the right, was doing the exact opposite of playing like that. Mata who, lets be honest, you're arguing was a 'right winger' made 11 crosses. Rafael made just 1 less, Adnan Januzaj in 30 minutes made 1 more, and Rooney, Young and Evra comfortably outcrossed him. He also made an equal team high 5 key passes.
So, in a team performance based solely on the tactic of crossing the ball and stretching the play the picture is clear. Mata did not make genuine attempts to get to the byline, he did not cross the ball as much as two players who were clearly playing as wingers (Januzaj and Young) he crossed the ball less than 1 of our full backs, and just once more than the other.
The irony is, that a playmaker playing off one of the flanks is a reasonably modern position, but its being slated as 'shoving Mata out wide' by people who presumably are also making the same argument that Moyes is a tactical dinosaur. Whilst I don't think Moyes deserves the defence it is very obvious that whilst Mata is playing games and we are not winning Moyes will be criticised for how he utilises him regardless of what he actually does.
In comparison, look at the heat map of a right winger in Valencia playing against Cardiff.
Clear differences.
EDIT: feck it MORE STATS.
United average positions vs Fulham
Do I even need to analyse this one or is it becoming obvious that its just an outright lie?