I don't think he has played 90% his IF role on the left tbh. All things considered half of the time he was as a CF or roaming forward for Real in his career there. He came from behind and attacked the box as much from the left as from the center or right. Sure as WF role he's more fluent on the left, but half of the time he was also Real's target man.
As a wide player I actually prefer him in his United form, rather than the LWF where he was more of a goalscorer and not the exciting winger/cutting inside winger. His overall best to me was 11/12 where he shared most of all traits - accomplished and great goalscorer but also tricky, wide, creative player.
As a team build around him he absolutely has to play as a LWF as that's his favorite role, but to me this team is build around Spain/Barca and Xaviesta running the show, which IMO is also equally devastating combination and a sound game plan.