First, our defense, IMO was not 10th best in the country last year- that is based upon total yardage given up. That stat was skewed by how slowly we ran our offense (one of the slowest in the country, typically using up nearly all of the game clock before the snap. This hurt our offense because it permitted opponents to get the last shift, which we could not adjust to.
However it helped our defense because they faced fewer plays against them. That made our total yardage given up stats look better. We forced few turnovers and we gave up a lot of key 3rd and longs.
FEI which ranks overall defensive efficiency, had us about 40th in the country. That said, I do think our defense will be BETTER this year in reality, whether it ranks 10th or better in yardage or not.