UConn has played in a BCS/NY6 bowl more recently than Nebraska and has over 20 guys in the NFL currently.
Diaco led teams were losing games by 30 with a first round corner in Byron Jones and a second round safety in Obi Melifonwu. Diaco's lack of ability to properly organize a program i.e. establish strong recruiting ties, hire good coaches/coordinators, and overly aggressive micro managerial tendencies did him in at UConn. Not to mention the fact that he's batsh#t. Jerry Kill had agreed to take the OC job at UConn this past December and Diaco said no. He was fired a week later.
The guy is perfectly suited for the role he is currently in. But if you turned the reigns over to him as head coach you'd find out very quickly he'd be in way over his head. And yes, you can look at his time as a HC and see that.