I agree totally with the general premise that the NFL can't evaluate QBs. I just don't quite buy the examples he uses to support it. Keenum would probably do better in Chicago and Cleveland than Glennon or Hoyer did, but he sure as hell wouldn't be playing like he is here.
With a few exceptions (maybe Brady, Brees, Rodgers and a handful at the bottom) every QB in the NFL rises and falls based on his system and changes to his supporting cast. That's why it's so important to get those things right before you try to develop one. And it's especially important to consider those things before you try to evaluate one.
Look at Alex Smith. For years, he was considered a bust (especially since he was taken 1st overall when Aaron Rodgers went 20-some picks later). They forced him to learn 6 different offenses in 5 years. I don't care if you're Joe Montana, that isn't going to work. And it's going to give you a false read on his true ability. He's in KC now with some stability and he's been to two Pro Bowls and looks like he's headed to another.