Well Asamoah didn't look like he'd play as a LWB before he came to Juventus. Asamoah is more of a CM, where as Bonaventura is more of an LM/LW. If Asamoah could have the qualities to play as a LWB, I can't see why a LW wouldn't be able too. Asamoah's defending isn't anything to brag about, I'm sure Bonaventura could do the same, and I believe Bonaventura would be better for Juventus going forward.
Bonaventura on the left, pushing Asamoah to the center would be great IMO. He would be some much added depth to the CM.