Diaco and Narduzzi aren't proven either. It's only been a year for Narduzzi and Diaco 2 without anything outside of a nice Houston win. Pony up for them? Not on those short term results.
I've given the example of Tuberville many times. Pretty successful coach but never had a conference record above .500 in 3 years at TT and that was after Mike Leach never had a losing conference record since his first year there. You never really know how a coach will do when they switch locations even if they've had success somewhere else. I'll caveat this by saying I still like Bielema and Strong and still think and have said they are solid coaches but look at some of the troubles they've had. How about Chris Petersen in his 2 years after all the success at Boise, he's doing just about what Sarkisian did before him although still early in his tenure, 2nd year. I'm sure the UW fans would think they'd have won a little more by now though. How about Rich Rod to Michigan. So you never know for sure outside of like a Meyer or Saban of how a guy will do when he switches spots.
I agree they're unproven, however, I would take their head start over a Coordinator that has not been a Head Coach. Narduzzi has worked with worked with less talent than Ash at OSU and Diaco would probably cost about the same as Ash with 2 years under his belt.