Jim McMahon and Steve Young played in the exact same Norm Chow offense that Ty Detmer did at BYU. The same offense that Phillip Rivers,Carson Palmer and Matt Leinart later came from with varying results.
BYU did not run the ball much at all when Detmer was there. AND.....they still relied on more of a short passing attack while Detmer was there.
Rivers had Chow as his O.C. for only his Freshman season. There were 3 more seasons for NFL teams to evaluate him in another offense.
At USC, Chow did use more of a vertical attack with Carson Palmer because he had a stronger arm than any QB Chow had coached. I saw Palmer shred Iowa in the Orange Bowl, and Palmer was making throws DEEP down the field that I haven't seen in any of the "spread offenses" that we have talked about here.
Here is the key point.
Chow doesn't have a "spread system" every year.
Chow changes his offense to fit his personnel. He puts players in position to succeed instead of getting players to fit into what he likes to do.