I think you're probably right about it being a bit of both. The top end on the SEC is clearly better than the P12, but I'm not totally convinced the middle to lower ends of the SEC are that much different that their counterparts in the P12. The last few years, Arkansas, Vandy, Ole Miss, Missouri, Tennessee, etc have been mediocre to bad. There haven't been much to judge by lately since the SEC rarely comes west. I know AM and UCLA split their last couple of games and Cal beat Ole Miss a couple years ago, but that's about it for middle of conference matchups recently