1.) when you're running all these run pass options, the linemen don't know if it will be a run or a pass because the QB makes a read and decides after the snap.. on a standard run play, you can have lineman past the line of scrimmage blocking someone, or looking for someone to block. It's a completely different mindset for run blocking. You're litterally trying to mow people down past the line of scrimmage. In a pass play, you can't do that or you get called of an ineligible man downfield. A pass play forces the line to step backwards to pass protect. An rpo, has to be treated like a pass, because the line doesn't know the outcome of the play, so it's not like they can just run people down.
2.) The qb doesn't have the same kinds of reads where he pulls the ball out of the RB's hands or decides it will be a pass play. Sure he has different kinds of reads, but you're basically running a play without thinking too much. You might pitch it to a guy on an option, but that's usually an easy read to make.
3.) Yes, if you understand Frosts system, the Defense is supposed to compliment the Offense. It's a quick strike offense built around putting points on the board quickly. To compliment that, the defense plays aggressively by design. This leads to more turnovers, sacks, and also busted plays. Because of this hurry up scheme on both sides of the ball, changing the offensive identity allows you to change the defensive identity to more of a ball control type of system. That was the old way we did it. Control the clock, march down the field. The defense played more read and react, and made the opposing team earn each first down and forced them to go the length of the field to score. This is a polar opposite to what we do now, and why the defense is actually doing good by giving up an average of 30 points a game. The offense is supposed to be averaging 50 a game.
Hope this helps.