There just doesn't seem to be a correlation between success in some narrow domain like engineering, business, art, or music and being a good human being in general.

I also wonder if there's a causative factor. When someone becomes super successful they tend to get surrounded by people telling them what a genius they are. That can definitely distort someone's self image. Could you stay balanced if millions of people compared you to a comic book superhero for years and loads of people did whatever you said because you had tons of money? Now throw in tons of stress and quite possibly a good helping of loneliness due to the difficulty all this creates with forming real deep relationships with others.

I don't see any particular correlation with being a bad human, either. Look hard enough at anyone and you'll find feet of clay.

Success in their domains greatly outshine the clay.