We have a major tactical advantage in midfield. Three man midfields have a big natural advantage over 442 and 442 became so rare. This is the reason 442 went out of style in the top leagues. Much has been written how packing the midfield with 3 players offers an inherent advantage tactically. The Christmas tree is essentially a variation on the 433 format and thus has this inherent advantage over 442 in midfield. We've seen this happen numerous times in the last 20 years and its why 442 are so rare now because they do have a distinct disadvantage in midfield against more modern formations.
"‘Look, if I have a triangle in midfield – Claude Makelele behind and two others just in front –
I will always have an advantage against a pure 4-4-2 where the central midfielders are side by side. That’s because I will always have an extra man. It starts with Makelele, who is between the lines. If nobody comes to him he can see the whole pitch and has time. If he gets closed down it means one of the two other central midfielders is open. If they are closed down and the other team’s wingers come inside to help, it means there is space now for us on the flank, either for our own wingers or for our full-backs. There is nothing a pure 4-4-2 can do to stop things’.
-Jose Mourinho
http://www.zonalmarking.net/2010/01/25/teams-of-the-decade-13-chelsea-2004-06/"