Reply having only read to page three: GSP trained Kyokushin, Chuck Lidell trained Koei Kan (sp.). Of course they all trained other arts its MIXED martial arts you dumbass. Everyone trains boxing punches because they are the best because boxer ONLY USE THEIR HANDS. Everyone learns BJJ grappling because they ONLY TRAIN SUBMISSION GRAPPLING. This does not mean that everyone else's techniques are garbage, just that in learning everything they watered down quite a bit. It can still be effective. Also top level MMA isn't the best indicator of style effectiveness, since at that point athleticism shows through, and everyone will be training in every style.