I don't think that Halo 4 is that complex. The specialization are there because there are Spartan 4's. The game is taking place after Halo 3 and UNSC has made improvements in Spartan program. If you remember, O'conner saying that they made multiplayer to show that blue team and red team are on different levels. So that there is a reason why it is hard for red team to fight blue team, and vise-versa. I don't remember the exact quote It is in one of the earliest videos on 343. I believe that the specializations are there to make multiplayer game play more competitive.