He sucked at Auburn after Malzhan and Newton left. That's why I think Sumlin may see some of the same problems. In the SEC, you aren't allowed down years and, if you're successful, your assistants will get better offers. Assistants are essential in the recruiting process. Does TAMU have the funds to keep the assistants? They leave, star player leaves and talent level decreases. USC, regardless of down times, is always a recruit draw.
And I won't even compare Vanderbilt to USC because I know that's silly. That's why I think the two SEC coaches finding unexpected success might be good candidates. Expectations will be higher for both of them at their respective schools.