John O’Shea has admitted that he has been scratching his head wondering why Arsenal allowed one player to leave under Mikel Arteta. Arsenal have got very little wrong in the transfer market since Edu and Mikel Arteta took charge at the Emirates. The Gunners have moved themselves into title contention. And they made an encouraging return to the Champions League this season. They have made some brave calls, letting the likes of Mesut Ozil and Pierre-Emerick Aubameyang go on free transfers. And some of their signings have proved to be inspired. But it is also probably fair to say – understandably…