Its only been one game so I think its too early to call him a flop or a bad purchase.
I'll check this thread again if he gets injured again or if he carries this form to the end of the season.
I don't think Wenger stalled his development or ruined him as a player. Too many fans, pundits and to a degree the players themselves, blame their lack of progression on Wenger and his methods. The truth is the person ultimately in charge of Chamberlain's game is Chamberlain, Wenger didn't go onto the training pitch and tell him to misplace easy passes and walk around the pitch out of position.
I think Wenger just had a blind spot for Chamberlain like he does most of our players, he treats them as if they are his sons. That notwithstanding, besides the injury problems, there's a reason Chamberlain never nailed down a permanent spot in our team.
EDIT:
Chamberlain, despite his wish to be a central midfielder, he doesn't seem to have much confidence in his ability to play there.
At Arsenal the two first choice midfielders are Ramsey (Injury Prone) and Xhaka (A player who hasn't fully adapted). After those two our options are less than stellar. Wilshere is further away from a first team spot than Ox ever was. Cazorla's career is nearing its end. Coquelin is out of favour and Elneny is a sub. Yet Chamberlain didn't back himself to get a midfield berth against that less than stellar competition. Then he goes to Liverpool where he will be further down the pecking order than he was here. I can't make sense of it