Then there's the situation where every player on offense has to understand their job, and how it changes, with each tell that's exposing something about the defense. Routes change, blocking assignments could easily change, timing changes, so many new things to consider and it all has to be done within one or two seconds.
These are the challenges that you face "after" you've learned what that defense is, and how to read it. You then need to be able to understand who the players you have on the field are, and their abilities, and tendencies. All of it, part of the QB's processing of a play before the ball is snapped. You don't get there without playing in games. You learn the concepts on the sideline, and develop the skills, on the field.