As an aside to this, PPG isn't the end all be all statistic anyways.
Team A plays 3 games and their defense allows 40 points on 40 total drives.
Team B plays 3 games and their defense allows 50 points on 60 total drives.
Team B's defense allowed more PPG, but they also faced 20 more drives against. Is that because their offense kept turning the ball over? Or because the offense couldn't sustain drives? Is Team A really the better defense considering they faced less opportunities against?
It's the same with offense. People keep pointing out that the Bills offense finished 7th overall. Sure, in PPG they finished 7th but in terms of the percentage of drives ending in points, they finished 15th.