A couple of remarks in response...
First, the RPI has been exposed for its faults. It can and more and more so is manipulated by teams/programs in attempts to enhance the chance to play in the postseason. To a part, however great or small, is not that what is occurring now with some of the very teams questioned from the big xii? How else do you explain a team with a current SOS at 39 [KenPom] also having an OOC schedule strength (weakness) of 332? Meanwhile, a team say like Iowa has played to the 36th best schedule (OOC 144th). All else being equal, it appears that today each team opposing TCU is playing roughly the same team as Iowa based on SOS - and to a degree RPI.
Second, ranking metrics can be flawed by preconceived notions regarding SOS, RPI, etc. The idea that the big xii is the best conference even at its lower tier simply because some algorithm might spit that out in October/November does not necessarily make it so.
The big xii has fallen into glory in spite of itself. The round robin play is a product of necessity rather than planning and sooner or later that is bound to change when either expansion or implosion of the conference comes about because of football. Ranking services prefer the totality of teams playing each other home and away as it removes some of the uncertainty in place in imbalanced scheduling. It should never, however, be mistaken as an automatic pass into being the best league simply because of the scheduling.