There is a massive difference between running a spread option and running a spread passing attack with the QB as the "runner" in a RPO passing scheme.
Mullen's offense was predicated on a mobile rusher who could be a threat to pull the handoff once the DE committed to the RB and rush around the edge for several yards.
RPO-based offenses rely on a mobile QB who can roll out of the pocket and throw from there...or pull it down and take what the defense gives you. Many, many teams run versions of that--including Bama, Clemson, and tennessee. The QB isn't designed to run 10+ times a game..but if that's what the defense gives him--they're encouraged to take it & quickly get out of bounds or slide to avoid a hit.
Frankly, it's shocking why Napier isn't trying to use AR's legs more. When he's scrambling for yards in the open field, he's incredibly dangerous...and forcing teams to spy him opens up other areas of the field that we can attack (especially via crossing route patterns).