I'm sure that folks want Rees to be successful. I hope he is! But you need access to offensive minds and real experience, not offensive tape to become proficient at game calling and game planning, both highly nuanced processes.
The fact remains that Rees' primary exposure to offense is his 7+ years in the "Kelly" offense (plus 1 year on the staff at NW plus 1 year on the staff with the Chargers, neither of which are exactly temples of offensive football.)
Unless one worships at the altar of Brian Kelly, that justifiably ought to cause concern....much concern.