The majority of Leviathan parties are successful. Over 90% But after 5 or so clears, people start playing sloppy and begin making mistakes and the party disbands.

Maybe 25% Of Turn 5 parties are successful. But they can only clear it once or twice before the group disbands.

Turn 6, About 10% are successful. Most can get to the slug phase but people never seem to learn and keep making the same mistakes. I question how a lot of these people managed to beat Turn 5.