Harvin is a toxic, selfish ass but I think we win XLIX if he's still on the team.
Not because he actually does anything, but because you have to commit resources to stopping him.
It's easy to stack the box and try stopping Marshawn. Gets a little tougher to stop him AND the thread of the read option keeper. When we're backing you out of the box throwing deep balls to ADB and Kearse, it gets even more difficult. And when you have to commit resources to stopping stretch plays PLUS all the types of plays above, sooner or later you're going to break.
Harvin wasn't the only factor in the two games, but I think you got a good sampler of what a difference it makes defensively for the other team in GB I vs GB II.