I'm not sure I agree with that. Steve Young played backup for a few years to Montana, before tha he struggled in other systems. Same with Testeverde in Tampa Bay, Cleveland, and Baltimore before being a success in New York. I see what your saying but it isn't always the immediate impact that ensures superstardom. Brett Favre waited for awhile.
On the flip side, Jeff Blake had a monster season his chance he got to start in Cincinnati, now he can barely make a team. Karim abdoul Jabar ran for 1,000 yards here in Miami his rookie season, then he just disappeared after that. So your theory isn't entirely accurate. Sage needs to be in a system that is right for him to succeed, just like most players. Time will tell if this one is right for him.