Sledgehammer and IW are two different entities. According to their website, Sledgehammer was formed in 2009, a whole year before IW incident. Sledge was commissioned by Activision to create a third person CoD game but amidst the IW incident, Activision had Sledge cancel/postpone the project and move in to help IW make MW3.
I saw an ad on their site about hiring for a new project. Most probably MW4 or the third person CoD game that I mentioned earlier.
Heck, it might a new CoD series or even a completely new IP.
And you're right on the balancing issues. CoD 4 was awesome but it didn't have all that many content. MW2 delivered content wise, but it's quality and balance was poor. I hated all CoDs after MW2, but I got them nonetheless, hoping "Hey, at least this one will be like CoD 4". Haven't played Blops 2 since I was here in Qatar when it released. (Gaming PC's back in India. Heck, I don't know if it could run it either. Treyarch's PC ports are quite shitty.)