TAA, a midfielder who has hardly ever played in midfield, Great argument! Let me explain to you why I have brought the point of attacking FBs to the fore. The way most of the teams play today, there is hardly ever space in the midfield today, they are compact, congested and well organised in the middle. As a result, majority of the space is available out wide. So, an attacking FB is afforded the time and space to make passes/runs and join the attack in ways it wouldn't be possible had he been playing higher up the field as an attacker or a midfielder. That is the biggest advantage players like TAA are provided with and you see them reaping the benefits. Trent wouldn't be half as effective if he played in midfield now. After 2-3 years, maybe but definitely not now.
Now, if we had been playing with both Bruno and Pogba in attacking positions together in a 4-3-3, it would have been different. But, neither Matic nor Fred are good enough as a single holding defensive player, hence Pogba stays back most of the time. Countless times you see AWB being provided the space to do something, he will make a lame back pass or dribble into useless pockets. An attacking FB in his position will not only provide an outlet for the attacker which Aaron does sometimes, he will also be able to make runs into the box to try to score/assist directly which he doesn't. Shaw had started to do that recently, although he still isn't that good in it.