I think the issue with Rashford, as others have alluded to, and the reason he gets criticism when his stats suggest it may be unwarranted, are that despite putting up decent numbers, he's an incredibly frustrating player who should be doing better than he is. This may seem like a harsh judgement, but there are multiple times each match where his decision making costs us. Whether it's holding on to the ball too long, or shooting from ridiculous angle, he so often denies us goal scoring opportunities.
I have the opinion that he's got potential to be a top five forward worldwide if he can address his decision making. He's as much ability as Mane, Salah, better than Willian, and potentially as good as Sterling, but they seem to utilize the ball better than him over the course of 90 minutes right now.