Ohio State could roll their competition if Braxton Miller is the Heisman-caliber quarterback so many believe he is, but I think this is unlikely. In 2012, Miller finished 81st in EPA+/pass. To put that in perspective, that puts him six spots behind Trevone Boyking, TCU's backup quarterback. But he does it with his legs, right? Miller did accumulate rushing stats, but he was only 38th in EPA+/rush among quarterbacks and in a virtual tie with Josh Nunes. Johnny Manziel was more than .3 points per carry better. He completed 58% of his passes and 40% on 3rd and long, and he was sacked on more than 10% of pass plays. His yards per completion were decent, but he was 56th in explosive plays per pass among qualified quarterbacks. I'm sure he's probably a decent fellow, but Braxton Miller is hands down the most overrated player in college football.
To his credit, Miller was a force in the red zone (5.7 points/possession), which allowed the Buckeyes to finish just outside the top 25 in points/possession and EP3+.
The defense finished in a similar position in points/possession allowed. They allowed a fair share of explosive plays and did little in their opponents' backfields, but they were generally solid against the run and pass and were tough on 3rd downs.
It's possible that Miller makes big strides in his second season with Urban Meyer, but if not, I don't see Ohio State coming close to some lofty expectations in 2013. The schedule is soft, but it was soft in 2012 as well and they still had a number of close calls. The model gives Ohio State a 5% chance of going undefeated again if they replayed their 2012 schedule (with the same 2012 team), and I would assume a similar probability of going undefeated in 2013.