I get that, but aren't you making that point in support of the bigger point that a QB can be accurately graded by the win-loss record of their team?
That's not how the people who work for NFL teams evaluate QB's. A QB can play better or worse than their team's win-loss record. Brees played a whole lot better than the win-loss records of a lot of his seasons. A lot of QB's do. The opposite is also true at times.
But don't you know that the QB is responsible for every defensive snap every offensive snap and every ST snap in a football game. He's even responsible for the temperature of the gatorade , ohhhh and the color as well. Sarcasm Off