But even those other groups you mention also aren't what they once were. For Matteo Messina Denaro to be able to stay on the run for going on 3 decades now, Cosa Nostra still has to be extremely, extremely powerful. There's no way around it. He's one of the most wanted men in the entire world. There's proof that he's even been visiting many other countries too which is nothing short of extraordinary in this day and age, and it's even been rumored that he has visited the United States. I don't know if that's true, but whenever he's finally caught, I think the revelations that come from it will blow your socks off.
I think the fact that Messina Denaro is on the run for that long isn't so much because of his personal power, but because the "higher-ups" protecting the mafia (politicians, corrupt law enforcement, freemasons etc) need him as a sort of "boogeyman" to divert attention from themselves. If he was arrested, many people would say "ok, the last defendant in the bombings/massacres of the 90s has been caught, now let's focus on whoever protected him and is still free", and that's what many powerful people don't want.
About the potential revelations in case of his arrest, I can't know for sure of course, but I think he only will be arrested when his replacement is ready, and whatever evidence and compromising documents he may have, they surely will already be safely hidden long before the arrest will be "allowed" to happen. When Riina was arrested, the police took away the surveillance from his home and allowed the mafiosi to remove all compromising evidence from it before the house was searched. When Provenzano was arrested, no big revelations came either...
