Ok. I personally love Martial, I think he is a class above all of our player's bar pogba. Like previously mentioned this is a dire team, rooney, ronaldo, tevez, berbatov used to be our front 4 nevermind our midfield and defence. This lack of quality not only affects him but all of our better players, e.g rashford, pogba, maguire, de gea as so much is expected of them.
For example, put the current de gea in the 2010/11 season and we win the league not lose on points difference. My point being those good quality players will bring the best out of the players. Rooney struggled in his last few years as the quality around dropped, not slightly but drastically and its no surprise that he had his last great season playing alongside RVP.
For Martial to prove he is truly worthy of United no 9 shirt, he needs to score more, he is to be fair to him great at linking up play and creating chances for others, specifically rashford. However, how much better do I think he could be? Personally I believe if surrounded by players of similar quality, which unfortunately we are severely lacking across defence, midfield and attack, I believe he could be deadly. I don't think he will ever be a 30+ goals a season striker. Not to say he can't achieve this a couple of times but in comparison to harry kane for example... But i do believe hes more than capable of 20+ and 15 assists. I believe he under-appreciated and the lack of quality around just like pogba frustrates him as the chances he creates for others are rarely replicated for him.
James and Mctominay lindelof shaw and wan bissaka have done well, (specifically wan bisska and mctominay who are great at covering ground and making tackles, exceptional even) but overall all lack the combined quality expected of united to create chances, win tackles, dominate possession, play cute accurate penetrating passes and dominate aerials balls.
frankly, put Martial and rashford and pogba into a quality team and they will thrive. these are the players we must keep and build our team around.