Look. There is some simple math in there. Morton played for 19 years. Aikman played for 12 years, and Aikman was a little frail. He's never going to win *any* QB endurance contest, sorry. Anyone, no matter how attached to the Aikman legend they are, has to realize that a pretty good QB who plays for 20+ years is going to score higher than Aikman.
The system the author used isn't going to reward a QB for 5-6 good years. It's going to be very favorable to the Jim Harts and Jim Fouts of the world, guys who play at fairly high levels for a long long time.
Bill James uses a system much like this one in his Historical Baseball Abstract. And so, players like Babe Ruth tend to float to the top, and Goose Goselin of the Washington Senators, who was a great power hitter for a few years, tends to be in the 30s and 40s and 50s of his charts.
As loud as people were putting this system down, I was curious and looked. I think the naysayers are wrong and the analysis is legitimate. It's driven by health of the QB, length of career, and overall performance, as opposed to playoff performance, but it's a legitimate look at QBs. For guys like a Dan Marino or a Kenny Anderson, this kind of analysis may be the only way to see their careers for what they actually accomplished.