Well, the sad truth on the Mafia is that there weren't really any dons as clever and powerful as Vito Corleone; you shouldn't rate real life ones with him. Some of the old school dons were very good choices, but as the years passed, most gangsters were like Sonny and Vinny: headstrong, careless, possibly bad tempered. It probably didn't lead to the downfall as much as Rico laws, but it certainly would have exposed the mafia a lot more, and probably would have affected it.