You really need to look at strength of schedule and the era in which each of the coaches you mention played.
Also, you need to consider the time it takes to change a programs schemes, recruiting and philosophy and the transition that takes place when you bring in a new coach.
Sometimes a program just needs to take that chance, but BYU is very unique. The program is close. Let’s see if they keep improving. This year will be a big indicator. A few tweaks here and there and an improved more dynamic scheme on Defense could make all the difference. If the team overall does not improve over the next two years, there will be a higher amount of pressure to change the staff, to the point it will probably happen.