He had all the tools, he achieved some success, but he never came anywhere close to having the kind of career that he was capable of. To me, Melvin Guillard looks like being one of those guys. :hat
Maybe Branden Vera, seemed like he was the next big thing then after his holdout never really wanted to fight to win again. now he just fights not to lose.
I don't know of Aleks other than by his reputation as Fedor's younger brother who is covered in prison tatts and has hep-C. (I think?) But I'm not at all familiar with his fighting abilities. I've seen him a long time ago against James Thompson I think, but as I recall that was too short a fight to get much of a read on how good he actually was. :conf :hat
I would say Mark Kerr. After he stopped taking drugs his career completely nose dived. Although being the number 1 heavy in the world during his prime -which was short- he never challenged for the PRIDE title let alone winning it. Lost to Fujita in the GP. And never won the UFC title despite being one of their biggest stars in the late 90's and a tournament champion.
Underachived or overachived? He was like the incredible hulk with his needle, without his needle he was david banner.
Underachieved as i believe he could have done more. Odd to think that a man who as ranked as the number 1 heavy in the world never won the PRIDE or the UFC title. But like you say without his drugs mentally he was just too weak.