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After Manila

 

After "The Rumble in the Jungle"; so 1974 (year of my birth ). Muhammad Ali no longer had anything to prove to himself, and nothing to prove to the world. He didn't need the health damage. He didn't need many to dispute his victory in the third fight against Norton (some also against Young). He shouldn't have lost to the mediocre Leon Spinks. The only thing Ali has proven (against Shavers) is that he has a great chin. Muhammad Ali would then retire as the lineal champion, which only Gene Tunney and Rocky Marciano had done before him.
Joe Frazier of course didn't know how things would turn out, and I understand his "hunger". Frazier would end his career with a win in that scenario. He would have a score of 1:1 with Ali, and 0:1 with Forman. Joe Frazier didn't prove anything after "The Rumble in the Jungle".
Joe Frazier without Muhammad Ali, and Muhammad Ali without Joe Frazier would not be what they are in the world of boxing history.

Something similar happened after the rivalry between Gene Tunney and Jack Dempsey.