Obviously you did not carefully read the list, as 42 is not a perfect score. In fact Ryan Fitzpatrick, who graduated Harvard, got a 48. While I believe that it is the highest score "achieved" by an NFL player, it is not the theoretical high score. There are 50 questions to the test, so unless they offer extra credit, 50 is the theoretical high score.
I also don't agree that the test does nothing. Not because I have an opinion, but because NFL scouts do. True a high score does not guarantee that the quarterback will become an elite player. Nor does a low score guarantee that the quarterback cannot succeed. But it is used by scouts and decision makers as a factor for drafting players. Some teams value it more than others. Does it predict how well a player can learn the playbook or make quick decisions in reading the defense? Some decision makers seem to think so, regardless of what you or I think. That makes it relevant. What a few talking heads on ESPN say, is meaningless.
Ryan Fitzpatrick has a very strong arm and has been fairly durable since he began his NFL career. He has also been very inconsistent and has thrown a lot of interceptions over his career. I don't think the score of 48 correlates with his career performance. Teddy Bridgewater has one of the lowest scores at 20. While still early in his career, he seems to have solved the Vikings problem at quarterback. While still has a shot at becoming an elite, he has a long way to go to earn that moniker.
While Michael Vick has been starting at quarterback for the Steelers, I would have preferred to see Ben Roethlisberger's Wonderlic score.