I agree with the sentiment but what you do need to factor in is whether Martial would have been in those positions to score against the same opposition when playing as the no 9.Lets be honest Ighalo has been good in the matches he's played, but it has been against low low opposition. Brugges and Derby are not exactly great parameters to make a decision.
That’s the key here. Does Martial have the discipline to stay central and forwards and the guile go keep making those runs and stay switched on for the 90 minutes.
In my opinion he doesn’t. He’s far better playing off the left wing but for almost identical reasons Rashford is better than him in that position as well.
That said our full strength 11 would have Rashford as the no 9 and Martial playing and linking up off the left.
My dream scenario would see us sign Kane as the no 9 and play Rashford off the left, leaving Martial as a sub to be honest. One can dream.