Independence eras. This is all games played, not just conference opponents.
When BYU was in the WAC- 66%
When in the MWC- 64%
Independence win percentage?- 63%
BYU is doing pretty well despite the honor code, despite being a private institution that won't play on Sunday, despite playing some big time opponents (probably more big time opponents than BYU has ever played), and despite the huge swing in advantages towards P5 conferences.