Except for Ohio State winning the natty in 2014, all of the other national champions going all the way back to 2006 have been southeastern teams (either SEC teams or teams geographically in the southeast like Clemson and Florida State). You could count 2005 if you count Texas as being in the southeast.
So of the past 15 national champions, the southeast has won 14 and the entire rest of the country: 1.
By the way, my state alone has won most of the past dozen national championships (6 for Bama and 1 for Auburn = 7 out of 12). College football really is a southern thing. The rest of the country just doesn't get it like we do.
Is a major conference still a major conference if all it’s power house teams leave and are replaced by mid majors, major a major conference a mid major? That said, Texas and Oklahoma have consigned themselves to future mediocrity in the SEC. Ask Texas A&M, Missouri and Arkansas how easy it is for former SWC/Big 12 teams to compete in the SEC.