People at the low end in skill do better on average, and people at the high end in skill don't do quite as well.
I think this is because streaks are quite a bit more lethal, and I think Treyarch justified making streaks more powerful because they lowered the reward that streaks give.
In previous games getting one kill with a predator missile gets you one kill closer to your next streak. In BO2 though getting 3 kills with a hellstorm only gets you half a kill closer to your next streak.