I used the "per 90 minutes" stats, in post above. Which had Mikhi 6th in the league and Mata 27th for key passes.
I know, but Mkhi has just 455 minutes in the league and half of that were sub appearances. 4 out of 15 his key passes were just in one game, against Middlesbrough, and 3 against West Ham. That's almost half of his total in just two games, during our best period of football. He hardly played when we were struggling to create anything, while Mata was our best player(during first few months).
So there is really no point in blaming Mata for not having more key passes per game when he is our third best in that and he is just worse than Mkhi and Lingard whose stats could be described as flawed.
I did the same for assists. Rooney was 12th in the league, Mata 68th (Martial 26th). No doubt you will put this down to luck. People often do when they don't like what stats show them.
It's not really just luck, Rooney was always quite productive player so it's not a coincidence he was involved in some goals, but Mata's assist again Middlesbrough was probably more important than any of Rooney's and Martial's two combined this season. I mean, Rooney has at least 3 assists this season where he passes the ball to a player who either scores long range goal or who beats few player and scores a goal(there was somehwere video of his all assists this season). Martial also has 2 assists like that in first game of the season.
It's not really luck, but you cannot call it being creative either, that's why assist don't really always tell you who the most creative player is. Mata should have one or two more assists this season though, altough he hardly picks any assists when the games are over, so that's on him.