Even with Taysom and Jamal 9-3 would have been a success. Then after one game where the team wins without Williams and loses Taysom by the third quarter, if anyone had said BYU would still go 9-3, most world have accepted that record gladly.
BYU then had to develop a qb 3 months removed from his mission. No easy task. They also had to adjust to the loss of Travis Tuiloma, at the time he was considered the MVP of the defense.
Tanner was and is supremely talented, but he had much to learn and did not have the spring to even start to learn the playbook. The defense was gassed by the end of the game against UCLA, but Tanner's pick was what lost the game. It was a misread, and had he thrown to the open guy, it was a likely TD and probably BYU wins.
Tanner has really progressed. He was holding the ball too long, and sometimes threw late, but he's getting better and better. He's going to be one of the BYU greats.
Potential is one thing, but this team had a lot to overcome. 9-3, by any objective measure is a successful season.