Asamoah is an amazing wingback.
The profile of this position is basically impossible to satisfy in every single aspect, you'd have to be excellent in both defending, crossing, dribbling, creativity, huge stamina,...
In other terms, you'd have to be a beast defender and flashy winger in one, not to forget being able to run for 90 minutes straight.
Asamoah fullfills most of these criteria perfectly, of course lacking in others as well, but that's to be expected.
Evra on the other hand seems to be a rather mediocre wingback to me.
If he was amazing, we would be scoring for fun.
But that doesnt mean Asamoah IS the problem. Maybe i used the wrong term in calling him "average", as he is no De Ceglie for sure. He offers us alot physically and has good stamina and even some nice offensive qualities, but like you said, the profile of this position FOR JUVENTUS is basically impossible to fill. Why? because we would need a super human who could press, dribble, trackback to our defense area to cover skilled enemy wingers AND then go with the ball at his feet dribble passing peeps and scoring assists for fun. At the same time letting Vidal and Pogba to play box to box at their will without having to cover that player. Impossible and unreal.
But this profile is impossible to fill because our formation is faulty. In practice, for our current 352 to be the force it should be, it would need a player like that to let tevez and llorente have some room by spreading the enemy defence and sending top notch crosses and passes, and to have Vidal and Pogba cover the back of said player. It will not happen.
Since is impossible for our wingbacks to cover all that ground during 90 mins... our formation always needs to be tight and pressing high on the pitch.. and our CM need to cover the wingbakcs when going forward BUT at the same time cover Pirlo.
This would work wonders if we had 2 world beaters in each wing who could dribble, assist and score on their own...but asa and Licht are not like that, and cant split the play enought, or be effective enought to make enemies mark them frantically and give more space to llorente and tevez. We keep wasting chances and possetion. We resort to throwing long balls because we cant score or threaten the enemy.
In summary, for this 352 to work, we would need our 3 mids to alternate covering the 2 amazing wingbacks. But in our formation, we want asamoah and licht to create chances, and on top of that we want vial and pogba to create. The first will not work because of our offensive limited wingers, and the 2nd will not work because of Pirlo