The problem with playing two pivots is that neither John Obi Mikel nor Frank Lampard are a dominant presence in midfield.
Chelsea are essentially playing a front four, so it must be counterbalanced with at least one elite ball winner.
Mikel is playing the best football of his life, so he's not the problem.
Lampard's goals (all penalties) are overshadowing the fact he's shirking his defensive duties. He's the one that isn't adequately protecting the back four.
It's a lot harder when the game plan isn't to park the plane in front of goal. Lampard is being exposed because he isn't a defensive midfielder. He doesn't function like a defensive midfielder.
This is where Étienne Capoue comes in.
The more you watch him, the more you become impressed by his physique, his winning attitude and his tackling.
This season, there's no comparison between Étienne Capoue and Yann M'Vila. Capoue is still going out there and trying to win back possession, whilst M'Vila is happy to just pass the ball 77 times per game and not get injured trying to tackle.