BYU was winning 10, 11, 12 games a year under him when he started and finishing ranked. BYU hasn't done anything in 5 years.
I don't think anyone is trying to compare generations here. Since he's been the HC, he's gone downhill in half of his tenure. What is the definition of decline? BYU isn't what they were even in the first few years he was here... That is what we call decline.