When he's confident on the left he contributes excellently to quick, first time interplay, shoots more from distance (which he's improved upon) and takes players on in the middle of the pitch to lethal effect. It was never much use for him to take the fullback on the right because he's never been great at final balls in crowded areas.
I really think there are pros and cons with Sterling on either wing that balance out. The big element of Sterling is his confidence, as you mentioned. When he's in the right mood he's world class and I don't think it matters where he is. When he's not in the right mood he's going to have the same problems wherever.
He's been more confident this season than ever and that's why he at times he's scored goals galore. His general play has steadily improved too. We need to do what it takes to help him flourish in that regard and keep his spirits up for a season because if we can he's a 35 goal a season player left, right, or both.