The history of BYU football spans more than your lifetime. It's 92 years of history...and yes, all the years (and coaches) count. We can't cherry pick to fit any particular narrative. Bronco is in 2nd place and it's not even close for anyone else below him.

LaVell Edwards: .716
Bronco Mendenhall: .713
G. Ott Romney: .571
Gary Crowton: .531
Eddie Kimball: .514
Hal Kopp: .486
Tommy Hudspeth .482
C.J. Hart .350
Alvin Twitchell 0.289
Floyd Millet .286
Tally Stevens .286
Chick Atkinson .279
Hal Mitchell .267

http://en.wikipedia.org/wiki/BYU_Cougars_football