As I see it, the key to Fu's offense is the RPO. The QB evaluates the defense and has to decide whether to run or pass, often making that decision after the snap based on how a key player (safety or LB) makes their first step.

If the line gets penetration he is forced to pull the ball out and look downfield, often under duress and with little time for the routes to develop. When that is the norm he is going to pull it quicker and lose the option part as the LBs and safeties don't respect it and don't crash the line since the line is able to handle the back themselves if he hands it off.

In the philosophy I described, the line dominates up front and the safeties and LBs have to make a decision....the QB has time to read them and react accordingly. They crash, he pulls it and has time to let the receivers (who are more likely in man coverage) beat their coverage. They drop and the back hits the line at full speed, meanwhile the safeties and LBs are changing direction to get back in the play. That's really no different than running the ball up the middle until the safeties crash then running a play action pass over the top other than giving the QB a chance to see a mismatch and exploit it (higher risk, higher reward). In both, you keep the ball, wear out the defense, keep drives going and get the occasional big play over the top.