If the program has 'declined' then LE was the one who started it and Crowton was the one who really put it in the basement.
Way, way, way too many BYU fans think BYU was a national power right up until Crowton/Mendenhall took over. The reality is that, other than 1996 and one game in 1990, BYU hasn't been a relevant team since the mid 80s.
I agree that Mendenhall is not a 'great' coach. But, honestly, 'great' coaches are few and far between and BYU fans who think that the program is so intrinsically strong that any average coach could come in and start ripping off 10 win seasons (like they did in 2006-2009, say) are kidding themselves.
A lot of the 'anti-Bronco' crowd love to tell folks like me to get my head out of the sand. Honestly, if they think anyone with minimal competency can win big at BYU, they're the ones with their heads underground.