I don't see many fighters being able to get Brock on the ground, yet alone beat him on the ground. Look at all the rolling and such that Herring attempted and Brock, only 3 fights into MMA showed great wrestling. We have to remember, he's LEARNING as he goes. I don't think Frank Mir catches him in that sub if they fight again, I really don't.
I'm not saying the guy is the best HW in the world, not by any means. However, he's a legit fighter and has the TALENT, not the skill yet, but the TALENT to be scarrrry good.
His speed, agility, endurance, and aggression will give him a chance against any fighter who doesn't have good striking. I can honestly say that give Brock another 3-4 fights under his belt, if he were to fight the guys you mentioned, I would take Brock.
Joe Rogan pretty much summed it up best. Brock Lesnar isn't just a HW, he's a guy that walks around at 290 lbs, cuts down to 265 and is faster, quicker, and stronger than any other HW. That is one scary thing to think about.
MMA in the aspect of talent is no different then any other sport. Alot of them work their asses off and become good athletes. Alot of guys are just GIFTED. Brock was one of those Athletes who was simply gifted with unreal talent and if he works as hard as the top hard workers, he will have a very succesful career, and one day hold the HW title.