Snooker and pool stance is quite different, so I don`t see how they compare.
Hendry had a a very stable stance, but so does Trump and pretty much all the other snooker players.
I don`t really think there is something unique about O'sullivan's stance.
For pool I like Immonen and Hohmann
John is the closest I've seen to Dan Louie, who got screwed down on the shot better than anyone else. You knew he was never going to miss and he rarely did. Buddy had the most solid stance among Americans and Ceuelmans had the most solid stance of anyone. He was/is a tank! One other player who was solid as a rock was Kim Davenport. Just watch a video of him sometime. Nothing moves except his arm until after the shot is complete. He locked down great!