From the CMU game moving forward, he has been quite impressive and he has been exposed to a pro-style offense & has made protection calls. Allen is not a day one starter, but he is much further along than Mayfield who has no exposure to a pro style offense outside of the Senior Bowl.
And comparing Air Raid QBs to pro-style QBs make no sense. The philosophies of these offenses along with the timing and route concepts are just different. It's like comparing a baseball prospect in Las Vegas to someone in Wilkes Barre. One prospect plays where offensive stats are inflated while the other is closer to what they will become. Plus Air Raid QBs have predetermined reads, Rosen, Allen and Darnold are making reads.
And it's not just QBs, Orlando Brown isn't asked to pass protect that long because the ball is out so quick. That is why his stock is dropping.
While I may prefer Rosen to Allen and Darnold, I would take all three ahead of Mayfield.