Marvin said:
he's more than a winger. His passing is excellent - as good as anyone at the club. There are very few English players who have his touch. Wilshere and Rooney and that's all I can think of at the moment
But he's not more than a winger, he plays only as a winger. If Mancini felt he was good enough elsewhere he'd have used him as a playmaker when Silva was limping through games. Johnson does have strengths (his finishing especially) but has far too many weaknesses to be a high level player. He's not eager enough to get involved in the game which is why he is anonymous so often and bombed when Mancini gave him a run of about 4 starts in a row.
For a tricky player he has no pace at all and his party trick has been found out so he only seems to get past a player 1 in every 10 tries. That's the difference between a Robben and a Johnson, Robben has the same trick too but is so fast and skillful that players still struggle against him even when knowing what he is going to do. Johnson is supposed to be a winger but offers very little from the wings, his stats are not bad but many of his contributions came against teams already beaten.
I can name a fair few wingers out there with more pace, more skill, and who will contribute more over 90 minutes - what you want from a winger. Bale and Di Maria to name a couple and I'd rank all three of United's wingers (Valencia, Nani, Young) as better players who have a greater impact over a season.
You have to ask yourself why it's Sunderland and Everton interested in him now, whereas once upon a time it was Chelsea and Liverpool. It's because Johnson has not kicked on even with Mancini urging him to work harder, and that's also why we're looking at £10million from him when we could have pocketed double that once.
The last straw for me was against Sunderland when we needed ingenuity against a team parking the bus with a narrow formation. Johnson played the entire game and injury ravaged Sunderland played Colback, a midfielder, as the full-back against Johnson. He had Johnson in his back pocket for the entire game - a young midfielder filling in as a full-back. As such Johnson didn't produce the variety we badly needed (width to counter their narrow formation) and we couldn't break them down. Johnson was switched to the left in that same game and still managed to produce nothing. A high-end winger would have at least created something that game, he didn't.