I don't think GSP was the best ever in terms of explosiveness and cardio. I don't remember his fights having a lot of action to be honest. He was the best at hiding his takedown behind a jab while also mixing in some karate kicks. Then after getting the takedown his opponent rarely got up (going off of memory here). That was his simple but very effective plan. It's not like many fights today with so many back and forth action where fighters are taken down, then get up, then get taken down again, then reverse the position, then get reversed again, then get back up and then get into a wild boxing/clinching exchange and on it goes. Fights are more evenly matched now, especially the midlevel fighters, and have a lot more action. I would guess that some mid ranked fighters who are wild and sometimes get caught with a punch or choke due to always pushing the action have a higher cardio output than GSP.
