My vote is that some are good businessmen, but most are not and just rely on threats of violence and crime to get where they are.

You know how they say there's something like 10 associates for every made man? Well those associates are one of two things: they are either a criminal without the smarts to become a made man, OR they are a business man who does have the smarts who got involved with the mafia for some reason (gambler, mafia groupie, grew up together, etc).