And this is part of the problem with QBR.
A. Neither QB had much of a chance in this game. Considering how both Olines played today, I would say both were at least mediocre. So, Im supposed to assume an "average" QB would have played better than either of these QBs today. With the pressure both QBs had today I don't think there are Qbs in the NFL who would have played better. Maybe Manning since he is a savant at reading defenses and can call his own plays at will at the LOS. So this goes down as poor games for both QBs when really if you watched the game and considered everything going on around them I don't think anybody could give them less than a C which is mediocre, or what should be a 50 on the QBR scale.
BTW.....the other thing it shows is the luck factor. Rodgers comes out slightly higher in the grade but had Joe not lost one of his two fumbles which set up 3 points or if Rodgers had lost one of his fumbles then Joe probably grades out equally, if not higher. Too many chance things like that that QBR doesn't measure.
Overall it's probably as good a measurement as their is... However, reasonable complaints like these are why it's like everything else... just part of the evaluation process.