That part was a "self fulfilling prophecy" and not due to the hard work that he put in to gain traction. That's what Whitey planned all along. He would inform on the (more powerful) LCN and get them all put away so he could become the underworld king in Boston. It worked but without him double crossing the LCN he would have been nothing more than a drug dealing pimp.
there is alot of truth to that, but at the end of the day, getting to the top of the criminal underworld by any means necessary seems to be the most important. we see this kind of stuff all the time with the mexican drug cartels, contacts in high levels of government being used to get a leg up on the competition. one thing that i think often gets overlooked is the fact that bulger seemingly got
WAY more information than he gave, which was one of the main scandals with the whole relationship: the fact that loads of intelligence related to the mafia was said to come from whitey, but never did. what info did he ever even give them? something about a making ceremony, some other smalltime street stuff?
my point is, that while whitey's relationship with the fbi definatly contributed to him being a top crook, i would argue that his organizations ruthlessness contributed just as much to their overall success. the streetgang/OC hybrid that was winter hill seemed to be alot more feared within their own community in and around southie, compared to the mafia run territory in the north end. with that said, both organizations were more than capable of taking out the trash, and i remember kevin weeks saying something along the lines of "the mafia has alot of teeth!"
