Of course he was, he won the ballon d'or here, but he went on to almost a decade of insane numbers and incredible international success, so he'll be always seen as a Madrid icon by the vast majority of neutrals.
How would people see Messi now, if he had played for let's say Juventus (just an example, regardless of their state at the time; an English rival club would distort the views) nine years ago with similar success as Ronaldo had at United and then went on to be the Barcelona legend that he is now? Which jersey would he be remembered in?