What matters is your percentage of wins, right? Yes - but it's also true that teams differ in the strength of their recruiting. What I didn't know until I read this article at watchstadium.com is that the strength of each incoming class is measured and ranked, just like teams are. Not surprisingly, there's a relationship: the better your incoming class, the more your team wins.
But it's not an absolute relationship (otherwise, why play the season out?) So if we compare class quality against the final record, this gives us a good way to measure the strength of coaching. For coaches, your input is the quality of your players, and your output is your win-loss record. Coaching is converting talent into wins. That's what you have control over. Not the strength of the rest of your conference, not how screwed up the ranking polls and CFP committee are. (A committee to determine who gets into the playoff? Ever wonder why they don't just use a transparent formula? It's so the bowls make more money. It only has to do with how good the teams are to the extent that if it's too obvious they're actually maximizing for revenue, people will spend less on bowls.)
So if a coach consistently wins less often than the strength of his recruiting class predicts, he's screwing up. If he ends up winning more often than the recruiting class predicts, he's taking silver and and turning it into gold, and he's a good coach.
The article I'm linking to shows scatter plots of programs from the Power Five, plotting number of wins from 2015 through 2018 against average incoming class quality rank for the same period. They don't give an r-value, but the curve does look sigmoidal. This is interesting, because sigmoidal curves often suggest network behavior, and the output here (number of wins) for each team is dependent on other teams. They also point out the relationship is weaker in basketball for a number of reasons including transfers.
On the plot below, the further above the line, the better the coaching. Bottom line: Mike Leach at Washington State is the best coach in the Power 5, with his team finishing 6 wins higher during 2015-18 than would be expected based on his recruiting class. Paul Chryst at Wisconsin, Kirk Ferentz at Iowa, and Dave Doeren at NC State, all tie for second best coach in the Power 5, finishing on average 5 wins higher than their recruiting classes. These are the coaches who are converting talent into wins most effectively.
Which coaches waste the talent they bring in? UNC and Maryland (6 wins lower), along with Nebraska and Texas (5 wins lower.) The full list is available at the article.