Yes, a QB could be argued to have the biggest affect on the game but even at that he is only one of 22 starters that have to do their jobs to be successful; and that doesn't include all of the special teams players and backups who affect a team's chances. By the winning as a starter metric a QB who wins on a good team suddenly becomes a worse player when he goes to a woefully bad team that can't do anything.
Great point Velo. Football is the ultimate TEAM sport and really, it makes me cringe to even hear reporters or others talk about how many games each "QB won in his career." That's like saying Nolan Ryan is a bad pitcher because he is supported by a team with a .101 batting average, and because the team doesn't win more than it loses because they cannot score any runs, it's all on the Pitcher. There are so many factors for a QB to succeed, including the opponent's strength, the health and effectiveness of the OL, the ability to have a running game to take the pressure off the QB and passing game, and the ability of your defense to get you the ball back. Football is a more complex game than basketball because you have to rely more on each other to succeed as a team. I say that, having played both sports.