I think it's a mix of ignorance and bias. I certainly rolled them together and you're right to note that, but I certainly think bias comes into play as well. I'm confident that if McCaffrey played for, say, USC or Oregon he would've won.
And while I'd say the SEC defenses are probably better in general, I'd also say the Pac-12 offenses are better, or at least more diverse, in general. I don't mean just pro vs spread, I mean the level of ability on each side. QB play in the SEC is really poor, for instance. But obviously these arguments could go around in circles. Finally, I think the Pac-12 was deeper than the SEC this year -- while the absolute ceiling for quality might have been lower, the floor was also higher. Other than Oregon State, basically any team could beat any other team in the conference. In that state of things, I think McCaffrey's numbers stand out even more.
Ah, well. Thanks for the thoughtful post in response.