We should be worried if Rooney takes over the spot of Martial while Martial obviously performs better as a 9 then Rooney.
Depay dropped atm is no problem, Rooney not being dropped while Depay is resulting in Martial moving out of his spot to accommodate Rooney? Insane.
If the team performs better with Martial on the wing and Rooney in the center, I don't see how it is relevant that Martial performs better as a 9 than Rooney.
Too early to say anything yet but to me the biggest difference seems to be the mental state and attitude. Until now, it seems that Martial is very grounded, calm and settled despite being much younger. Memphis is rather the "I made it lets go crazy" guy if you want so, who seems to lose focus quicker and needs to settle down first
Well, that's just my amateurish armchair analysis based on the last couple of months
I think Depay is still quite immature, both on and off the pitch. He's not very sensible in his communication, allthough he's actually quite modest in everything but his long term ambitions, he comes across very cocky. And there are also unwritten rules like don't stand out with your fashion if you don't stand out on the pitch, this is of course a nonsense rule, but that's how it works. A more mature and sensible guy would keep a low profile in all the irrelevant things. I don't think Van Gaal has any complaints about how hard he works and his mentality in training, but hard work doesn't guarantee end product.
Martial is the more allround gifted player, he just has a superior ball control, very close control, and is very athletic. He had an excellent start, the pressure is off, and he can just use his general ability which is good enough to not lose possession, to beat defenders and score goals. Depay has never been and never will be a player who can keep the ball at his feet waiting for the defender to make a move and then dribble away from him. He's got his first touch and a sharp turn, but he's got to make it work at the higher pace of the PL, his timing is off, he can't relie on his tricks anymore and that's unsettling his game. Often he shakes off a defender, and then he's surprised there's another defender already or the first defender has another go at him, he still got to adjust his timing to the pace of the PL. If he manages that, his confidence and therefore his crosses and shots will come back. But this is the first difficult spell of his career, so he will have to show real character and mentality to get through.
Depay can become a very effective and valuable player, but he does not have the potential Martial has. Depay can become a star, Martial can become a superstar. Depay needs to be given time, Martial doesn't need time because he's so talented, but as a young player he will have some more difficult spells in the future to.