Basically you are both correct.
SEC and southern football is better than other conferences and regions over the last decade and a half.
But disqualifying results for other conferences are not disqualifying for the SEC and that is an unfair advantage.
For instance .. the SEC brags about having to play good teams week in and week out. This acts as an excuse for the week they emotionally aren't ready and lose or just play a bad game and lose. The top teams in other conferences just don't have that luxury. They have to be perfect and the SEC doesn't. It's a huge advantage. When you are in the other conferences and play your championship game, you are not getting in with a loss (Clemson could actually be an exception this year but only because they are Clemson and not one of the other schools). In the SEC you don't have to win your conference and as we learned, you don't even have to win your division, to make the playoffs.
And that is where equality of opportunity comes into play. When Utah is the best team, or arguably the best team, they didn't get to play for titles. When TCU was arguably the best team, they didn't get to play for titles. When the SEC gets a non-divisional winner into the playoffs it takes a spot from a more deserving team/school/conference. When you are guaranteed the opportunity, you are gonna win a bunch of titles and when other teams do not have that same opportunity, they won't.
In other words, using the results from a system rigged for the SEC to make the point that the SEC is great, is fallacy.
With that said, the South is dominant in football right now. Absolutely in my opinion. I think it keeps getting worse because of culture and popularity in the respective regions. California and the West is moving away from American culture, of which football clearly is. The North East has always been a professional sports area, less focused on the college game (and let's face it, it is hard to recruit to there). Football is ingrained in the South in a way that it isn't elsewhere. Midwest is closest but still has a ways to go. No doubt about it .. the South is where the best players are generated, and where the best teams are at the moment when looking in aggregate.
So you are both right. I would just say the discrepancy would be a lot smaller in the form of championships if the SEC didn't have the built in advantages it has over all the other conferences.