Still not a very good metric. You completely write off anyone who hasn't been a head coach before, and you also essentially write off most coaches who make waves at smaller G5 schools, as well as coaches who needed some time to turn around dead programs, etc.
Mark Helfricht has a 70% winning percentage, a Pac-12 championship, a Rose Bowl win, a National Championship appearance and a top 5 finish in 3 years as a head coach. Justin Fuente had a 26-23 record and one conference championship before being hired at Virginia Tech. PJ Fleck had a 30-22 record and one conference championship before being hired at Minnesota.
I don't know about you but I know which one of those three I'd pick last as my head coach.
You and I are talking about different things. I am positing that, in hiring a new head coach, your chances of that person being a good coach aren't increased by them having already been a head coach in the past, and that first time head coaches and hires who have been head coaches before have about an equal amount of potential towards success. I'm disagreeing with the myth that we need a proven head coach.