The problem with comparing the situation with GMac and AJ in 2010 is that AJ, as a redshirt freshman, didn't offer a different skill set in the passing game/game management department that was employed at that time. In other words, they were the same kind of qb.
Sure, in hindsight, we see that AJ was a more talented passer, but in 2010, it probably wasn't that obvious.
The sitation now between Jalen and Tua is totally different. JH is a running back playing qb. A slightly better Nick Marshall. Tua, on the other hand, is a totally different skill set. He's not a bad runner on a RPO, but his skill set is basically a drop back, pocket passer.
The thing that makes sense about allowing Tua to play right now is that the type of offense we run actually fits Tua better than Jalen. Tua can run the RPO aspect, but he also can drop back in the pocket, go thru progressions of more than one read and then he can deliver the football on time and accurately.
I'm not saying Tua ought to start over Jalen against Clemson, but I'm just pointing out this isn't like a Gmac/AJ situation where both basically have the same skill set. Jalen and Tua are just two different types of Qbs.