There are a lot of "check boxes" on Coach Kelly's quarterback sheet which determine who gets the keys to the Rolls Royce. Some of these boxes are pre-snap, some are post-snap, some are intangibles like confident "presence", some are practice work ethic, some are mental toughness, etc etc --- you can add in more. I believe that one of these "boxes" becomes a near absolute in Coach's mind: pre-snap understanding of the defense and how the offense should adjust to attack it.
Why? Well, this would be one area of Coach's "philosophy" that people could, for a change, have an honest disagreement with him, but he seems to have so much confidence in his systemic design that he feels if the quarterback can just get us into the correct attack mode then even a marginally good QB can move the ball and score 35-40 points. Pike and Collaros, even with their wildly different styles had this in common at Cincinnati. They both were REALLY smart about their offensive systemic powers and reading the defenses' games. As I say, we can debate Kelly about going with the better pre-snap offense manager rather than the poorer manager but greater athlete, but I'll bet that he is weighing the plusses and minuses of that sort of choice all the time.
Andrew Hendrix [or Everett Golson] needs to get to Tommy Rees' level of understanding the pre-snap game management. This is what I think that people really mean when they say "understanding the offense". These guys are football smart. Learning the playbook can't be what's holding them back. What Hendrix needs is every snap against "surprise" defense that he can get and then show that he has the calmness and the instincts to get us going in the right directions. If either Hendrix or Golson [or Kiel] can do that, then Kelly will shift down to the next set of boxes labelled things like "fast release", "escapability", "running ability", "accuracy", "distance throwing", in whatever priority ranking he has on those [I'd bet "fast release" and "accuracy" are ahead of "running ability" even there --- see Pike].
I'm hoping that all four of our QBs can get their heads around pre-snap offense management and we can get down to a more raw talent way of choosing the starter. If they can get there, we all know that Tommy will be back-up [maybe even the guy who gets the bulk of the "extra reps" during practice] while whoever does not win the Hendrix, Golson, Kiel sweepstakes gets only a special package offense at best. I see nothing stopping Andrew Hendrix from being that "winner" if he can "get it" on the field in the heat of the action. Kelly, afterall once said that Hendrix has the quickest release that he'd ever coached --- that's a big deal with the boss.