I think it's pretty clear that Oswilers play regressed as teams got more tape on him. He struggles to read the D and holds onto the ball too long, two things that Manning doesn't do. The Chargers had Osweilers number as he continually missed blitzes and misread the D. Manning comes in and tears them up.
With th a healthy Manning the Broncos have to be the favorites to make the Super Bowl. The Broncos have played against 6 of the playoff teams and have won 5.