Jevohn Miller turned himself into a serviceable linebacker for one year, I believe as a redshirt senior. Problem is, that defense was BAAAAD and as improved as he was, he was far from a game changer and was never going to be. And when you invest 5 years into a kid like that to essentially get a one year return, you need like 30 of those guys to peak at any one time in order to field a winning ball club.
On one hand, I can see why he was loyal to CPR. He reached his potential under him and it paid off for him personally, to the extent of which he was naturally capable. He was probably proud of the growth he achieved, as he should be.
On the other hand, come on man. A little self-awareness and humility should and usually does accompany such individuals at ISU. Campbell upgraded the talent immediately across the board, even in his first year, and that was fairly easy to see.
I think we have two very different definitions of serviceable.