Some I would add to your good choices: CRUISERWEIGHT Evander HOLYFIELD v Dwight Muhammad QAWI II MINIMUMWEIGHT Ricardo LOPEZ v Saman SORJATURONG
When I think of unbeatable on a certain night I have to go with Mayweather on the night he beat Corrales.
Of the heavyweights who came before Joe Louis, I don't think any could beat the Gene Tunney who beat Dempsey the first time. Even guys like Joe Louis, Marciano and Larry Holmes would have had trouble with someone as smart, strong, and durable as Gene.
The Corrales fight was at 130. Do you think that PBF would have been unbeatable against peak Alexis Arguello at that weight?