If the ultimate goal is championships they were much better off in the Big 12 than the SEC. They were only competing with Oklahoma and Texas each for the Big 12 title. In the SEC they will be going up against Florida, Auburn, LSU, Alabama, Arkansas, and Tennessee. I see all of those programs and probably Georgia as more likely to get to the SEC title game and actually win the conference than A&M.
Tennessee and Arkansas aren't there at this time. If you include them than you have to include Texas Tech and Mizzou from the Big 12. Those teams are EXACTLY the same. And than you throw Okie State in the mix too.