A key part of a midfields job is to get the ball to their wingers. The difference between Angel and Valencia is that one is just very good, so he will do better things with it. That said, if we play Valencia instead, we just give it to him all the time too. He has just been doing feck all with it.
It is still just the players doing their jobs I reckon. And even if it were the strategy, and Di Maria's job was then to create for Falcao with it, can it not be said that the team is built around Falcao instead? After all, we got a ball winner to win it, to give it to a ball user, to give it to Di Maria, just so he can give it to Falcao. Perhaps he is the most important then?