We've been watching the same games completely different mate. Lost the ball the first 5-7 times he got it against City. Whatever you think he made happen in the City game, I'm failing to see. Even if he created half a chance, it'd still be terrible compared to the balls he lost. 0 goals, 0 assists. And 0 shots, even off goal against City. You've also written "in the city games", suggesting that there's two games against City he's been involved in. He was only involved in 45 minutes in PrL.
Against Hull, he had promise, but was inconsistent too. I had to refresh my memory, so I took a look back on all his actions. He had two good dribbles, one where he was faulted by Huddlestone, going past some players - Showed some signs of the Dortmund Mkhi. And one that lead to a free-kick just outside the box. Nice and all, but then take a look at the terrible efforts on goal. Two shots that's slowly running into the keepers hands, and a goal-opportunity where he thinks he has time to stop and shoot instead of just hitting it first time. He also gave the ball away a little too easily on some occasions - Clearly not where he was supposed to be. Had the except same trades from the City game, suggesting that he hadn't improved in that aspect. I can understand your sentiment of trying to play a player into form with regular game-time, but of course, I can understand that Mou didn't just give him the next couple of games - pretty important games, when you think back to the pressure Mou was under. Why take such a chance, considering his game against City?
Your other 'honest' question I think is too limited and speculative. Any player can come off bad, and any player can come off great from the bench, so it's hard to make any case that this is something all players would struggle with. If you asked me the same question with Rashford or Chicharito, you could argument the other way.
What I think is more important is that Mkhi seems to need to get used to the physical aspects of british football - Over time he will probably cope better, but he's been too easily brushed away under pressure. Had great games recently, but this is something he needs to work with. Seems he has gotten used to the pace now.