The very best players in the world are able to grab games by the scruff of the neck and lift their team when they are not playing well.
Sanchez has been a great example of that with the way he has regularly made things happen for Arsenal on the days when they have been average and have needed his help to help set the tempo in attack.
There is no way you could say that Di Maria has done the same for United while they have been short of their best form.
Yes he still works hard but, if anything, his performances have been getting worse, not better.
I highlighted on Match of the Day a couple of weeks ago how easily Di Maria was being knocked off the ball.