I'm sure the list of high level mob rats that we don't know about would surprise us and that there were a lot more than revealed, but 50% is way too high. Also, considering the era they were alive in, we can't dismiss Frank Costello and Carlo Gambino outright as rats just because they were successful. Law enforcement was all over them in the later part of their careers and Costello even had to do some prison time. Now they may have ratted rivals out in their path to the top before they became a major law enforcement target like we know Luciano did, but there is no evidence.
Luciano received a 40 year sentence and was doing his time like a man till his friends cut. deal to get him out, Gambino was harassed constantly after Valachi testified, and they even leaked. taped conversation between him and his wife to harass him in the newspapers. They treat rats different. Greg Scarpa was given immunity to do as he pleased for many years, same for Whitey Bulger. The rats are never pressured publicly or privately, unless they stop giving info. If Gambino or Costello gave "Tidbits" as a few like to try to get others to believe, they would have way more demanded of them to keep them out of prison. Underobess would go away, and in the old day a few small pieces of info would have never sufficed. The fact is the Mafia thrived for one main reason: No rats till Scarpa. Anastasia's brother is sad to have gave info after his brother was killed, but how true is that, and who dis the actually give up? Answer: No one.
