In the rawest of win shares analysis, the quarterback gets 100% credit for every play he is involved in. McNabb throws a screen pass to Westbrook that goes for 65 yds and a TD = McNabb throws 65 yd TD bomb. Campbell throws football off of Fred Davis' facemask and is intercepted by Sheldon Brown = Campbell throws interception.
By this definition, league MVP
Peyton Manning was worth +7.44 wins. That literally means that the Colts win percentage increased by 744% due to all the plays that involved Peyton Manning last year.
McNabb was worth +1.67 wins. Campbell just +0.39. There's a difference (his name is DeSean Jackson), but, even in the rawest sense of winning and losing, they were in the same tier in 2009.
In 2008, Campbell was worth +1.24 wins and McNabb was worth +0.47. Again, same tier. One isn't decisively more winning than the other.
Peyton Manning, Kurt Warner, and Drew Brees are in a different stratosphere in terms of producing wins and losses. McNabb is just a guy, clearly.
Advanced NFL Stats -- McNabb, Career