IMO, some people need to understand what makes a coach proven. Being a successful coordinator does not equal proven head coach. Winning games, winning small conference championships does not equal being a proven head coach. The best way to become proven is to win a Super bowl or national title, and even doing this once is never an a absolute guarantee ( though, most of the time, coaches who win the big one, stay consistently successful ) that one has become proven.
In another thread of mine, I allowed for big conference championships to qualify as being proven, but allowing that standard is not near as fool proof as winning the big one. Usually, you win a big time conference title, you go on to consistent success, but this standard is far far from absolute. There are many examples of coaches who won big time conference titles but within 2 to 5 years they are never heard from again.
Off the top of my head, the only proven head coach that was available last year was Jimbo Fisher. I wish we had backed thr brinks truck up to his home and beat out am for him. But, here I am spending someone else's money, which i have no ability to do. It's nice to talk about, but not within my power. I have no idea if we had the funds available to outbid am.
Scott Frost and Mullen are, by the evidence, further along than Pruitt. I wouldn't label either as proven, though what Mullen did at ms st was very impressive. On scale of most likely to get it done, Jimbo ( Jimbo's main obstacle is the fact that the goat resides in his division. Gonna be tough Jimbo, getting past them ) was #1, a proven coach. Mullen was #2 imo. I have very little doubt Jimbo will have sustained success at am. I have more doubt that Mullen will have sustained success at FL compared to Jimbo. Yet, no doubt in my mind Mullen has sufficient evidence backing him that he was the best candidate, other than Jimbo, if a program was looking for the best CHANCE at getting back to the top.