That's true, but maybe he could surprise us all. Not in terms of pace, but in terms of decision making as he wouldn't be able to resort to his usual "cut inside on to the right foot" routine and maybe he'd become less predictable this way. He could also take advantage of a more attacking full back on the right (he misses Shaw and Rojo is useless in attack) as he's currently not good enough to make an impact on the wing without another player drawing the attention away from him. He's never going to outpace most defenders, but could become a very dangerous player if he improves his decision making.
Sitting on the bench is not doing him any good in that respect and won't increase his confidence either. I'm not sure what Van Gaal's plan is, to be honest. I know he's benched because the other attacking players are performing better than him, but even Van Gaal said that you can't improve if you don't play.
He's a frustrating player. His talent is obvious and you feel something could happen when he's got the ball, but most of the time his decision making fecks everything up. He's mostly been shit on the left and with Martial being a fecking God, I don't see why we can't try him on the right or at least more central. I think he was a striker in the 1-2 win at Watford and did very well, using his physicality and technique and was far less predictable there. We just need to find a solution, because I just feel he could thrive somewhere else where he's the main man just like he did at PSV.