I agree with this. One of the reasons why Merchant said that Mike Tyson's style does not lend itself for a long reign of dominance.
Hopkins proves that wrong in every fight. There might not be a better fighter out there when it comes to timing and punch resistance in one. Id say its stamina...clearly stamina actually.
Reflexes, stamina and ability to absorb punishments . . . reason why we see big changes in fighting styles of active aging fighters.
Leg power. Without it, you're a dead duck. Of course we have to take under consideration that all fighters age differently. It all depends on how much of a beating have they had during their career.
i'll have to pick floyd too. not only because of his better boxing fundamentals, but also because of his elusive boxing style he's never been seriously damaged in a fight . regarding the topic.. reflexes generally is the first one to go when a boxer gets old.