If there's one thing the NFL has an abundance of, it is defensive coordinators who learn very, very quickly. Every time offensive football inserts a new wrinkle into the game, it usually takes only a year or two before the coordinators figure it out and shut it down (stuff like the wildcat comes to mind).
The same can be true with sensational rookies. Once they get enough film on Watson to learn his NFL tendencies and develop game plans, then we can accurately judge his body of QB play.