I am not sure he is better than Evra at LB. The LB position shows Evra's advantages compared to Asa (tactically better as a defender, crossing) and hides Asamoah's advantages (mainly stamina). With the WB thing, it was a different story.
Also, if we are going to keep playing the current system, then our midfield is running thing again since Pereyra is moved to AMC/RW. And since Vidal is out of form as well, we could really use an extra athletic midfielder.