Dak's success is easy to understand. Most quarterback busts are MENTAL busts. To be a pro quarterback you need a pretty good level of general intelligence to learn the complicated offensive systems, but you also need to be able to make snap decisions very quickly under pressure when your opponent is actively trying to give you false clues about how they're going to defend each play, which is a completely different kind of mental talent. You also need a very high level of emotional stability - things constantly go wrong in football games, and you need to be able to move on to the next play and not let penalties, drops, fumbles, cheap shots, taunting or the defense giving up plays to put the team behind with little time left upset your equilibrium. But temperament and intelligence are often completely disconnected things - there are plenty of calm morons and excitable smart people, but neither of them should be NFL QBs.
All that is kind of just the tip of the iceberg. Being a pro QB in the modern era is a very specialized job that almost nobody has the mental make-up to accomplish. And by the way, nobody knows how to scout for these things in a meaningful way. Dak is simply one of those guys who has everything from the neck up. He has a mind for football. Team draft QBs based on who has 1% more arm velocity or 1" of extra height or a 0.1 second faster 40 time because that's what they can measure, but none of that means very much.
You can point to Dak's situation, but this team had a bunch of guys in basically the same situation last year that totally crapped the bed. Would Zeke have helped them? Sure, but they would have still all been stiffs and the team would have been just a more competitive loser than they were, because those guys were mentally incapable of surviving as an NFL QB in 2016. Adrian Peterson never made the Vikings matter outside 1 season when Favre was playing like it was 1996.