Mata has seldom been played as a number 10 this season but when he has, he makes Lingard look like a championship player.
According to Transfermarkt, Mata has been used as an attacking midfielder (as opposed to a right winger) in the following matches:
Man City home (we created nothing, then sub Lingard on for Mata hit bar), Leicester away, Bournemouth away, Norwich home (poor team performance), Southampton home (half time sub), Stoke home, Chelsea away (Lingard scored), Sunderland away (team horror show), Arsenal home, Watford home (scored free-kick), Man City away (assist for Rashford's winner), Palace home. Also 4 EL matches (1 assist v Midtylland), 2 CL matches (1 assist v Wolfsburg), 2 FA cup matches (2 goals) and 1 League Cup game.
I'm not convinced by Lingard but Mata has been a near total waste of time this season both out wide and when used as a no 10. For a player who has taken penalties and a few free-kicks, his productivity is underwhelming to say the least. And I'm struggling to recall a long list of chances he created that our strikers have wasted.
As for Lingard, clearly he needs to do a lot more in the final third, show some imagination, better quality when he attempts a cross, more composure when shooting, make sure his first touch is decent, get stronger so he's not knocked off the ball so easily.