When Mikey took over, the Dookies were coming off of three straight NCAA tourneys under Bill Foster. Preceding Mikey were Eddie Cameron, Gary Gerard, Harold Bailey, Vic Bubbas (who is widely regarded as the guy who brought the program to NCAA tourney prominence), Bucky Waters, and Neil McGeachy. All but McGeachy won consistently. Did Mikey do great things? Yes. He continued an established winning tradition and improved the program. But, he did not inherit a program void of talent or name recognition.
Did Dean Smith underachieve? Yes, for the talent he had. He inherited a great program from Frank McGuire in 1961.
Did Roy Williams underachieve? Yes, while at KU...IMO. However he took over at UNC from Matt Doherty who all but ruined the program. Roy inherited great players and won the title his second year there.
Ask yourself this question. How would Billy Tubbs have done if he'd coached at Dook all those years with all that talent? Or Tom Izzo?