He's done all he can do in a less than competetive era but its his longevity makes him an all time great for me. Staying at the top is a great accomplishment. Everyone knows his weakness is a chin, well no ones really managed to outbox him and land on it for about a decade now. Sure some of his voluntary defences have been poor but if he beats the latest crop of heavyweights (Wilder, Fury, Pulev) then I'll forgive him for it.