Guiliani said once, "We turned the MOST POWERFUL organized crime group in America into JUST ANOTHER organized crime group in America."
Was it really THEM who turned it in just another organized crime group? I think it was more the consequence of the natural death of extremely powerful and charismatic characters like Carlo Gambino, Tommy Lucchese, Philip Lombardo etc that did the work, rather than the law enforcement. I can't know for sure, of course, but I think that if those characters were still alive and in power through the 80s and 90s, then the mafia would be weakened only in the 2000s. Human society is too corrupt and hypocritical to allow somebody like Carlo Gambino to get a life sentence or 100 years. It was difficult enough to give life even to a stupid thug like Gotti.
Law enforcement would be the second biggest reason for the decline of the mob, only behind general attrition.
And I never understood what people mean when they refer to the old bosses as "charismatic." Yes, by and large the old guys were smarter and tougher than their successors. And that's because they were a product of their time. But let's not forget they benefited from their time in ways their successors couldn't, i.e. less scrutiny from law enforcement, attrition hadn't set in yet, etc. So the gap between the old and new guys may not be as wide as some may think. You put a Carlo Gambino or Tommy Lucchese as head of a NY family today, or any time in the last few decades, and without those benefits, and they probably don't look as good.