If Bsu was getting beat up against good teams they would have some of these inexplicable losses. After years of tight games where BYU has been ahead a lot and actually been better statistically, I think it’s hard to say there is much of a gap between the two teams.
The gap in record is due to who they play largely outside of a couple bad years from BYU. Remember Bsu has beaten only two p5s ever in the road so they would be losing a lot of these p5 road games