Rashford grew up playing as a winger, Martial had success there for LvG.
Rashford grew up as a winger but showed his best performances as a striker - even more as a poacher under LVG. Reverting him back to a winger is going backwards. Likewise martial played as a LW because Rashford broke through centrally as a striker mid way through the season - therefore LVG moved martial to the left (also to cover Memphis) & Lingard the Am to the RW as a mid-season tactic whilst they all broke through.
Martial - Rashford - Lingard was what LVG was left with mid-season. Next season just by pure strength LVG would have played
Martial - Rashford
Lingard
That's all if's & buts - however martial was always a LF, LS or St. When he played LW he was covering as discussed multiple times on this forum with French league watchers who watched him grow up for Monaco.
Rashford for me would not have broken through to the first team & maintained a spot as a left or right winger - atleast not without him fundamentally making a name for himself as a striker.
They all show a plastered approach to being a winger - this includes Lukaku who has the best crossing of the bunch. They can cover it - but Martial's, Rashford's, Lukaku's strengths lie in being strikers - that goes from there ability to play centrally, their ability to play off the channels & wings when needed, their ability to drop deep, there abilities to beat the line, take their man on, play one two's to beat the defence & fundamentally their clinical finishing which is underrated (possibly except Rashford who has lost his touch ever since becoming a winger again - the position he just simply is not good enough at & especially not as a target man for Jose)
If you think the best way to get the best out of these 3 players is by playing them consistently on one wing further away from the goal - you will see like martial that their ability became very easy to read as they are consistently playing through the same direction & trying to beat defences from the same angle. Play them off the centre as a LF would then they play against the CB instead of the fullback who are well capable to defend against the likes of Rashford martial & Lukaku playing on the wing.