What will likely be seen with the SEC is teams knocking off teams.
You've got
Alabama
Oklahoma
Then below those two
Georgia
and then the occasional
Florida
LSU
Then a jumble for the rest.
Well those schools now will be knocking each other off. Texas can beat Georgia, FL, LSU. Oklahoma can sometimes beat Alabama and vice versa, and al the rest.
So schools that were starting to become accustomed to winning are suddenly going to be looking at loss filled seasons.
Conversely, if the BIG 12 schools remain and add, you'll see some schools move to the top like a Clemson has in the ACC or rotating schools in the PAC. The more they win, the better recruits/exposure etc. And those programs become similar level powers.
Really exposure will be as important as anything for the schools on top.
But in a few years the BIG 12 reconstituted will have undefeated or one loss champions competing for national titles just the same as now--will just be a different team or teams.
Meanwhile the Alabama's and OU's could find themselves with multiple losses instead.