However I'm not familiar enough with boxing to understand the example and so you might be saying something else. Can you elaborate on why you chose Ali and Spinks as exemplars, and what you perceive to be their differences?
When Spinks beat Ali, he was the quickest to win the title in history. He also was the only man to take a title from Ali. He was younger, faster, in better shape and had a longer reach than Ali.
However, despite the physical attributes favoring Spinks in every way, and the previous victory, in the rematch Spinks was completely destroyed by Ali, who trained hard for the fight this time.
These two are perfect examples of elite athletes with excellent physical similarities that put their careers on similar trajectories when you compare their early careers. However, Ali's mental talents and training skill so far surpassed Spinks that Ali only lost 5 times and won the title 3 times, while Spinks lost 17 and only held the title once.
Physical prowess matters, but not as much as training at the elite level.