I'm not buying that he made the most money independently. It isn't crazy, we all know he's been mad successful independent but there's a list of guys who just had bigger followings on the underground...
They did bigger shows, had wider reach, more people bought they drops, before they linked with majors. Even though Slim has stayed indie, for instance I refuse to believe he's made more money than Master P on the independent, underground grind. P owned a store and was popping in two time zones. And P not the only one...
Slim has probably stayed relevant longest but this is really more a result of his other hustles rather than just Slim as a rapper. Not that it's a super long list, but there's too many names to throw out there who did that indie grind at a bigger scale than Slim...