Yes he has been used in that position, I concede that point, for me he was Argentinas best player at the World Cup, but he is far too forward thinking to be considered a cm. he is definitely attacking. Uniteds attack would strike fear into most. Arsenal need to start playing two up, a target man with a paced player off him which with fully fit squad we have options in abundance just never have everybody fit. Defensively and in midfield we are strong again when fully fit.
I personally want to see a defender who can play cb and lb, a dm to offer flaminis bite with artetas passing ability and a left winger in order to force Wenger to choose between Cazorla and Ozil and play whichever in the central position, pointless playing both with one so obviously uncomfortable in the faster paced wide left role. Oh and a striker, not necessarily a big name but a strong team player.