Sanchez has been awful, there is no denying it. Martial has suffered as a result of this, never being given a run of games since while Sanchez has been allowed to play himself into "form" for 7 months now.
This is Alexis Sanchez we are talking about remember, a standout player at one time on the league. And apparently setting up a few goals in those 7 months justifies his near undroppable position in our team. People go on about Martial FC but what about Sanchez FC? He has done nothing at all as a Manchester United player to justify starting over anyone.
Jose dropped Pogba last season v Seville so why can he not drop Sanchez for a run of games. Or shift him to the right and make him earn his place once again? It might do him some good, reignite some hunger for a player who is capable of so much more.
I like Sanchez, I like Martial. Neither have been good enough since January 2018 yet, for the most part, only one is rightly criticised. The other is allowed to stink up the place week after week, there have been games where Sanchez couldn't not make a pass to save his life, would fall over constantly and play like he was half cut on a Sunday morning. Martials worst performances haven't yet reached that level, and he's been awful at times as we all know.
Of course both have had the odd decent showing for us, Sanchez v Spurs in the FA Cup, Martial v Chelsea in February.
If both can reach their best, either play alongside each other or in competition, then we as a team benefit.
To add, Martial looks like he will benefit far more from Shaw becoming integral than Sanchez, off the far fewer minutes Martial has played on the left so far. Something to consider.