who would you say have been the most naturally gifted fighter in mma that did not train up to their potential and could have reached far greater success had they gotten their heads staright and trained harder?
First nth American black belt to get the style nod from old man gracie IIRC, went from "the next big thing" to just burning out (might have been something to do with his missus overdosing). There was a point where it looked like Kang was going to dominate anyone at his weight class, he was looking crazy and then it all just faded away, all the big names pushing him faded into the background and he turned to a shadow of the fighter he should have been.
Penn because of how skilled he was. He had everything you want in a fighter from a skills standpoint. -Elite boxing with underrated kicks/knees. The flying knee he nailed Sherk with and the high kick on Diego were just beautiful. -Elite and creative BJJ. The liver kicks from back control to set up the choke on Florian and the jailbreak on GSP spring to mind. -Great finishing ability (the only other fighter in the lower weight classes [155 and under] who could hold a candle to Penn when it came to finishing elite opponents is Aldo). Excellent blend of KO power, submission skills, and killer instinct. -Great takedown defense. -Very good takedowns (name 5 LW's that could take down Fitch and secure back control. I'll wait.) -Amazing durability - he has a granite chin and prior to the Diaz and Rory fights (in a weight division he had no business competing in anymore) I don't think I had ever seen him cut. The lack of a real strength and conditioning program (minus his time with the Marinovich's which unsurprisingly resulted in two of the best performances of his career against Florian and Sanchez), refusal to gameplan, and poor response to adversity were his downfalls. Amazingly talented fighter though.
Honorary mention for Dave "Pee Wee" Herman. I don't think that he had the most potential in the history of the sport, but the brief flashes of talent he shows in his fights are sadly overshadowed by what appears to be total disregard for taking the sport seriously.
Other than those that have been mentioned (especially Penn and Randleman) I'd go with Duffee. Although I hope that he can rectify that with a good return.
Fighting skill wasted potential: Penn, Aleks Emelianenko, Rampage Athleticism wasted potential: Guillard, Randleman, Bob Sapp
