I'm not saying it doesn't work. But teams that have successfully used it have been very unique and 'complete' so to speak. And you're wrong in saying we have the right players for a 4-1-2-1-2, it's just the easiest formation to fit all of our 'star' players in which makes people automatically assume it's the best.
Di Maria is first and foremost a winger, he had a brilliant season as CM for Madrid that's right, but that's for Madrid with wide players such as Ronaldo/Bale, CM's such as Khedira/Alonso/Modric and an all around striker in Benzema. He will be ineffective for us in such a role, we lack the squad quality of Madrid. 4-3-3 will work for us much more than 4-1-2-1-2, you need to think of rotation, injurys and form, you really think all of our players will be fit all season to allow us to play a 4-1-2-1-2 in the first place? As soon as 2-3 of them are gone the 4-1-2-1-2 becomes IMPOSSIBLE to play. Also our front men are primarily lone strikers, I can't see any of them being able to work in front two for us.
4-3-3
De Gea
Rafael/Valencia - Jones/Evans - Rojo/Smalling - Shaw/Rojo
Blind/Carrick/Fletcher
Herrera/Carrick/Fletcher - Mata/Rooney/Di Maria
Di Maria/Young - Falcao/RvP - Januzaj/Young