battling for the starting spot. Because of Taysom's experience, running ability, leadership, and all the injuries he had to battle through, Taysom was going to get the starting nod unless significantly outplayed in the preseason by Tanner.
I believe they wanted to name a starter early - KS and Ty both said multiple times they wanted to name the starter as soon as possible - but they held off for as long as they did because it was a hard decision. Remember, Taysom wasn't named the starter until about a week before the first game. If Tanner wasn't bright enough to pick it up, and was light years behind Taysom, the decision would not have been hard and Taysom would have been named the starter weeks earlier than he actually was.
Tanner could not have been far behind Taysom in the preseason, if he was even behind him at all.
I think people starting these rumors about Tanner's inability to run the offense are doing it to defend Taysom out of loyalty.