Look at Auburn. Sandwiched between two mediocre 8-5 seasons was one 14-0 National Championship season built on the arm and legs of Cam Newton.
Hate him if you want, but he carried his team from mediocre to amazing. BYU with a player like that could make serious noise. BYU's glory days were built on a dominant QB.
If Tanner lives up to the legend, he might be that QB