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.