In Martial's first season he played from the left.
Also look at Mbappe, he is originally a striker but does all his work as a Wide Right Forward, cutting in.
Martial is a LF which is different to being on the LM - Jose has consistently told him to touch the line & prefers him holding the width considering that on the other side was primarily Mata - an inside AM. Jose historically likes one winger to cut in & one winger to provide width. Something martial is rubbish at.
Martial was a striker under LVG - playing centrally. Due to the makeshift introduction of Rashford & him having good performances - LVG played martial as a LW & Lingard as a RW whilst Rashford was a striker. Rashford was the only one playing in his position due to the number of injuries that happened midway through the season. Martial was never a left winger - his goal against Liverpool seem to convince people that he is. He was a central striker that drifts off to the left channels.
Mbappe is much more of a direct player than martial - mbappe is fast and takes his players on in strides & benefits from having the space & time to do so. Mbappe being asked to defensive work or being asked to stick to the touchline which is one of the main things Jose asks would not help him either. Martial on the other hand takes his players on by short distances & makes small moves to get past central defenders - the reason why he struggles against fullbacks who tend to struggle against players who use pure pace and running in to space over anything else.
Mbappe & martial share absolute nothing in familiar apart from being French - one is martial & one is a much more like Rashford - a direct player with the ability to play off the wider channels. All three would struggle under Jose because of the restrictions he puts on many attacking players like :
Playing in positions that are wrong or not purely beneficial to the player individually or as a team like martial, Rashford Lukaku could all be positioned better also inclusive of better position of Mata Sanchez & Pogba that would benefit the team.
Defensive restrictions of the attacking players when the defense & midfield is already significant defensive - as seen by mbappe who was constantly allowed the freedom to find the spaces attackingly on the right as a counter attacker; taking a prioririty in attacking over defensive work even though it was not bad.
Mbappe was not even that good for PSG playing in the RW - definitely decent however but primarily due to his directness. Martial is neither direct as a striker nor as a left winger - he is a striker that would benefit from playing next to a direct striker than asking him to be a direct striker himself ie a central support striker that plays off another forward allowed to take his man on & have options to either side.
Either way - comparing mbappe to martial & making it seem martial is a failure is wrong - mbappe is better than Lukaku & Sanchez was at his age & I would argue is still better them whilst the first two are reaching or at their prime. Martial is clearly not in José's plans of building a team that's gets the best out of him is not going to happen. That's why we won't win the league because consistently players like Lukaku, Martial, Rashfprd, Pogba are not playing in a formation & method that gets the best out of them - more a representation of trying to be a new Drogba, a new lampard, a new sneidjer etc - all these players we have different strengths & weaknesses.. Whilst we try to get them going in a 4231 - wouldn't you say we try find a formation & tactics that get the best out of our top 11 players rather than trying to build something that isn't there? To me martial is in our best 11 players - however he is not a LW & both martial & Lukaku would improve if they played in a striking partnership.
That's why I ask fans who are doubting martial - are we actually playing Lukaku to the best of his ability by asking him to be a target man or would he be better running off on the channels whilst someone like martial could be asked to tease & take on their central defenders. If Martial failed at this I would chuck him out the door - however him failing as a LW is more our fault than his. (even though he has done alright as a makeshift left winger)
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It is true Martial would be better playing off a striker. Changing the way we play and the system just for him though? Not happening.
Read above bro - I believe nearly every single player from Lukaku, Martial, Rashfprd, Mata, Pogba, Valencia, young, lindelpf, Bailly & many more have the ability to be better if we fixed a formation that highlights their pros rather than their cons - Lukaku's first touch as a target man is just most obvious.