Before UCLA, Tanner played more freely, and he showed he is a gamer. It was backyard football, played by a freshmen (albeit more mature) that didn't have the complete system down. In preparing for UCLA, Anae and Co. coached Tanner to play more within the system, throwing more intermediate and check down routes, giving what the defense gives you. This was a conscientious coaching decision.
You have to also consider that Anae's system had to shift philosophically once Taysom was hurt. All through preparations from Spring to Fall camp, the offense was different than the system Tanner is now running. And the cherry on top of all of this to consider is that Tanner hurt his hamstring, which is considerably more hampering than the original post on this thread could ever give it credit, and said injury is to his back leg that uses to drive the ball (ask any QB how important this leg is).
He is not regressing at all. Let's move on to the next Negative Nancy post since there's nothing to see here...