We only consider those teams roughly equivalent because they don't face each other every year.

With all those teams in the B1G, we would definitely see some sort of stratification take place. Who knows where OU and Texas would fall, but they might not come out on top. It's in OU and Texas' interest to stay in a conference where they can minimize the number of losses they get each season while still having a viable path to the playoff. And that's pretty clearly in the Big XII, not the B1G.

Also, it's worth noting that the B1G champion has been left out of the playoff for the last two years, while the Big XII champion (with the exception of the year where the Big XII was cowardly and awarded a "co-championship") has always gone to the playoff. The pond that OU and Texas are in is plenty big.