i know that there's more evidence regarding the weak chins of hearns, and jones jr, but louis definitely belongs on the list of ATGs with suspect chins and punch resistance(i can't see someone like max schmeling dropping or stopping any modern top 20 heavyweight today and these guys are worst than ever). rank these 3 chins from glass to iron.
Hearns. Personally l discount RJJ having a glass chin because of his age, him coming down from heavy (not many fighters go down in a weight class after going up), and not knowing when to quite. But in his prime his chin was fine.
Hearns and Jones would NEVER been able to absorb the beatings that Schmeling, Marciano, and even Charles subjected Louis to, as well as Louis.