I would say Rory looking strong is due to him training *smarter not harder* with some of the best in the business at cultivating wrestling strength.
GSP and Rory manhandle ppl and look really strong because they have the best training methods for developing that type of strength. Anyone could develop the strength GSP and Rory have if they only knew how.
Developing that kind of strength isn't as easy as doing squats or running a lot. You're using different muscle groups. If a person took the time to study human anatomy and recognized which muscle groups were most important in successfully executing a takedown. Then, experimented to figure out how to best target and develop those muscle groups to their full potential -- they could probably enjoy a big advantage over others who aren't willing to go to those lengths.
I think at some point GSP and his trainers may well have done exactly that. That's the reason why GSP's legs are so massive in comparison to everyone else's and its also the reason why GSP and Rory have such dominant wrestling and top game.
Bingo! They train very differently from most. It's all functional strength, cross fit, and gymnastics. From what I know gymnasts are p4p the strongest; arms, shoulders, abs, core, back, quads, calves, etc. Body builders are more powerful, but we all know it doesn't quite translate to real striking power ala Super Mario. I do believe Overeem is one of the few exceptions because he trained in kickboxing and has the techniques. When he ballooned he just became "The Specimen." Roids along won't get you that...you still has to work hella hard in the gym to maintain it.
Marcus Aurelius: Tell me again, Maximus, why are we here?
Maximus: For the glory of the Empire, sire.
Baked, not fried... the healthy choice.