The fact that you would even bring up Tuiaki as a comparison to Nua is embarrassing. Are you seriously putting Utah State, Oregon State, or Utah on the same level as Michigan and USC. Nua was hired at both positions by himself, he wasnt brought along by friend as his DC.

If USC wins tonight, he will now have been on two different teams that have been to the College Football Playoffs in …. let me check my notes...the last two years. Get back to me when Tuiaki had anything resembling Nua's resume.

You can know someone is capable in the position that their in (just like people bring on temps to a position and then hire them to that very position as a full time employee), but there will still be a gamble elevating someone to a higher position. You have to look at performance indicators. Nua has been successful at each stop. Major programs have taken notice and put him in those positions. Michigan and USC both have been big spenders on bringing in top coaches from around the country.

The fact is many P5 programs elevate position coaches to coordinator positions. Yes, a good portion of those are internal hires. But external hires do happen and have found success. Can hiring DCs from lower schools work, of course. But that is also a gamble - what staff can/will they bring, how will their defense translate to harder competition, how will they recruit, etc.