It was obvious that when Sanchez was signed Martial was going to play on the right. Sanchez hasn't played on the right since 2013/2014 and he has shown his best football on the left or as a striker. Sanchez is arguably our best outfield player and there is no way Jose was going to play him on the right.
It's something Martial needs to come to terms with.
Exactly, it's modern day football. Players have got to be able and willing to play in a few positions for the team and do each one equally as efficient.
If people feel Martial is only able to play on the left, well that's not good is it? Especially since he's still raw himself on the left, he has to adapt for the team, not the other way around.