Could their numbers be inflated? Maybe. You operate under the assumption they are, which is presumptious, especially since the more reasonable explaination for the decrease in their numbers is the fact Tebow and Bradford missed time with serious injury, rather than defenses figuring them out.
Colt McCoy is a better metric to use here, as his numbers decreased last year as well, and he was a Heisman canidate in the same era as Tebow and Bradford.
However, if we use McCoy, your premise is still false, since McCoy had much better numbers than Stanzi (30/12, 3,500 yds), finished on a 13-1 team, had the benefit of national hype and exposure, and still only finished third for the award.
If anything, Greg McElroy would be a better canidate than Stanzi. While he played in more games than Stanzi, he had an approximate amount of attempts. They are close on yardage, and both have 17tds. McElroy had 4 ints, however. Plus, he plays on a team that won the title, and has a shot to repeat.
I bet if someone came around here saying McElroy for Heisman, they would be laughed off. However, I like his chances more than Stanzi's.