Not sure if he would have been a good coach but I would have loved to have hired someone who would have allowed him to continue to run the D his way.
As for being a HC, his record with Detroit was 29-52 but Belichick's record with Cleveland was 36-44. Better, but not by a whole lot. When you take into consideration that Schwartz took a team from 0-16 to the playoffs in 3 years, I'd say not as bad a HC tenure as most make it out to be.