I think if the records broke the way you said, then yes, BYU would beat out most 2 or 3 loss P5 teams, but when was the last time we had 4 undefeated FBS teams? That would be a staggering number, especially with conference championships. Yes, BYU was predicted to have the best chance of going undefeated, but that was calculated at 21%, which means there is a 79% chance of it not happening. Fairly long odds, but the best odds in the country. BYU has gone undefeated exactly once in 111 years, its just not that easy to do it, and to get 3 other teams to do it is going to be pretty tough.