Is size directly related to strength? It does. But unless you have X-Ray vision, you can't see the size that matters in those sports!
Is size directly related to strength? I am sure they have a good amount of muscle mass, though. It is just hidden under a think layer of fat because these guys don't care about aesthetics or being "lean". I think it would be hard to find a skinny guy who can bench 275lbs and squat 6 plates.
Is size directly related to strength? That really only applies to the super heavyweights though who don't have weight restrictions. It would be more advantageous to stay lean in any other weight class.