The whole point of wanting the Big12 to represent well is for how it plays into conference perception so that BYU can get a bump in rankings.
If BYU gets a better bump in rankings in the second scenario, then the first scenario becomes unnecessary. At least in short term perception.
One could argue that the first scenario is definitely better for BYU short term, but the second scenario is potentially better for BYU (and CFB) long term by helping even out the perception of the different conferences so that the SEC/BIG have less of a stranglehold.
But overall, my feeling is that with the ever-changing landscape of CFB, I’ll take the definite advantage over the potential one. (“Bird in the hand.”)