That is my definition. They will rarely singlehandedly win you a game. They aren't going to have gaudy 2nd half or 4th quarter or Game Winning drive stats. They are the product of the team built around them and can excel at times. Anyone who is a "game managing" QB in my boom would never be considered a franchise player or QB. They are just a cog in the machine, although an important one.
You want them to run the offense and not fug up.
Game managers, seriously? A game manager doesn't win multiple superbowls and MVPs. A game manager isn't the best player on the team which both were at multiple times during their careeer. Game managers aren't difference makers, they "manage the game" and let others make plays.