re: There should be a tier structure in the SEC

Correct. SC was a later entry into the SIAA, and an earlier entry into the SoCon (about a year after the conference began operations). The SEC began operations during the Depression; I’m guessing economic conditions of the time (and the fact its main rivals were also east of the mountains) kept the ‘Cocks east. They would become charter members of the ACC in 1953, but I’ll leave the reason that they left to someone that has more knowledge on the subject (I do know that the NC schools played a part in that, and that Clemson would have left as well if they had any backbone).