Well according what you've stated, why isn't Hurts, Lamar Jackson and Purdy ranked higher? All of them played under better coaching than Dak has ever played under, and Purdy and Hurts have better overall talent around them than Dak has.
So again, why aren't Hurts and Purdy ranked higher?
Then you said "HIS playoff failures attribute to the lower ranking". Well this list was created by people who understands that NFL football is a TEAM GAME and here's why..... Hurts led Eagles won a Superbowl. Purdy led 49ers went to a Superbowl.
So according to what you've stated, apparently players THEMSELVES aren't judged by TEAM GAME playoff results, because Hurts and Purdy would have been placed higher, correct?
To conclude, teams win games, not single players. This list backs that up. Those people are NFL executives, coaches and scouts and they know how this game is played.