I read a Jose quote about playing Martial centrally in coming seasons if he does stay. I think it is his better position because he just can't cut it as a pure winger. One of his best games this season I can recall was when he and Lukaku played together away at CSKA.
So if the manager is feeling this it could be a bit of reassurance for the player.
Sane, Sterling, Insigne and Salah are fantastic players in their own right, even before moving to their current teams. It's very presumptuous to assume Martial would just automatically improve like them. He didn't really shine in the last European tournament despite having all the support and favorable tactics. Actually he was benched most of the time by Payet, despite his excellent debut season with us.
Lastly, the attacking versus defensive setups is a matter of opinion. Mine is that a top player should adapt to his current managers tactics. And it's not as if Jose's system prevents attacking. Tonight we saw several counter attacks and later on close range intricate passing buildup. Even though it was a newly promoted side, Martial didn't shine. As I said before , part of the issues is his supporting cast but what more conducive setup does he need? Knockhart and Gross had terrific games against the leagues second best defense Tonite (us). And that was even after they sat back . So for me i just don't buy it. It's just an excuse
Edit: link to CSKA highlights