A few people have posted inside info that Tanner has had difficultly grasping the offense and especially going through his progressions and anticipating receiver movements.
You have to remember the Tanner we saw last year ran an incredibly simple offense. Basically he rolled right and threw up jump balls over and over. Because of the situation we never got a chance to see him run a real offense.
I think we all agree that Tanner is probably a much better pure passer than Taysom and obviously willing to take more risks. What we don't know is what kind of mind he has for the game. (Heaps could make all the practice throws too.). Ty's offense when ran correctly requires a fair amount of knowledge, anticipation, and expert timing.
If Taysom has truly been much better than Tanner at making those reads we might be in trouble. Because, we've seen how good Taysom and receiving corps have been running things and it hasn't been pretty.