Oklahoma was not much of a known program as they are now prior to formation of Big XII in 95.
I don’t want to compare BYU to Utah but since you went there… unless the PAC-12 remains relevant, when USC and UCLA leaves, then yes, Utah dominating the PAC-12 can make an impact. BUT the problem is they haven’t and don’t look like they will be a relevant conference. So winning the PAC-12 won’t mean much after they leave.
The Big XII is ready with the addition of the new 4 programs to continue with solid football. And hence the door is open to a premier program to rise to the top. BYU can be that team. Not saying they will. But they can.