Coughlin is a good example. He was never a coordinator at any level. His record at BC was good but not outstanding. But he was a competent CEO type HC who ran a tight operation. He was up to the task of being a pro coach, which is actually a skill few coaches have.
Of course, Coughlin was tutored by Parcells, while Kelly is so wonderfully self-taught. So it's not apples to apples. But there are similarities in style, discipline, and organization. And I bet NFL teams think Kelly can at least manage the job, which is a priority in a world where the Mark Trestmans and Jim Schwartzes--tremendous X's and O's guys--wither when they become top dog.