We need to expand the pool of potential coaches and inject new life into how we recruit, practice, train, etc. Taking coaches from Utah State, Boise, Southern Utah, Weber, etc. will only get us so far.
Would I love a DC from a top tier university to take a "lateral" move to be BYU's DC. Sure. I just dont think that's likely. Not just from a salary perspective, but all of the other challenges that come - such as not placed in a recruiting hotbed like Texas, Cali, FL, etc.
I think its as much of a gamble to take a DC from a lower tier program. Sure their defense might work in a small pond, but what about in the Big 12 or against strong P5 schedules each year. I would rather take a coach that has been in an elite program - seen how they operate, practice, recruit, prepare players for the draft, etc. I want someone who can bring with them other people that have been in those programs.
As far as USC's defense - the parts that Nua was involved in - Rush defense, sacks, etc. were significantly better than BYUs.