Martial is an inside forward-type winger.
He's not a number 9. Most of his goals last season actually came from wandering into the edge of the box from the left or right wing. I can count probably 5-10 goals from inside the central box area last season. Give a proper world class number 9 that position and they'd score 30-35 per season. Martial got 23, which is about his ceiling. It's not a bad return, but if we're Manchester United, we want the best, and the elite. I want 30+ goals from my number 9 if he plays 50 games, otherwise, we'll keep stalling in and around 3rd-6th positions.
He doesn't have the ability to play as a top level number 9. I'm talking Leawandowski, Kane, Haaland, Cavani..... they're proper number 9's. Cavani has strolled into this team and put on a masterclass on number 9 play. Martial won't score the goals Cavani did yesterday, because Martial wants the ball in to feet, not smashed 5-10 yards ahead of him at 100 miles an hour.
Martial is a top player from the wing, though. He in my opinion needs to rotate with Rashford & Greenwood on those wing positions.