That’s an interesting point. If we compare Hayes’ time(s) against times of other sprinters at the time, and see if he or Bolt (or anyone else) are further away from the ‘norm’ (which we’d need to define), it would give a measurable way of discussing who is “faster”.
The highest ever rated chess player, Kasparov, once said that he considered Fischer to be the best chess player of all time, because Fischer was so much better than his opponents than any other champion. This could have him being modest, however.