I can tell you the reason Navy's quarterbacks look more effective is that they are usually going up against lower level competition than Tech faces. I know there are exceptions to that but follow my logic. If you noticed in the Navy bowl game the QB kept the ball many times and took a lot of hits. Now he is a pretty tough man and only had to sit out a few plays when he got his eye poked. When Navy plays Norte Dame they usually go through couple of quarterbacks to finish the game.
Regarding Justin, he is just too small to take the punishment. He could hold up against a Elon or Duke, maybe even Virginia type of defense but the tougher defenses like UGA, Va Tech, Miami and Clemson would put him out of the game after a series or two. He is quick but he is not elusive. I hope we find something for him to do, even if it is on defense. Unfortunately, it looks like he will be standing on the sideline for the next two years minimum unless Vad gets injured or the new kid comes in and is better than Vad. In a way we have either wasted a year of Justin's eligibility or the fact is he is just not good enough to be on the field full time.