(a) this is obviously a totally unanswerable question, in any objective sense
(b) but the fact that someone CAN win a bunch of medals in swimming (which is clearly true, and clearly not possible in at least some other events… say beach volleyball), is tempered by the fact that people very rarely DO win a bunch of medals in swimming.
It’s also pretty insane the number of Phelps’ medals that are golds.
meh, I would think that longevity at the top of your sport would be a good measure of the “greatest” but as always these things are subjective.
So I look at someone like Andrew Gaze, 5 time Olympian in basketball as a good model, now there are better players [90% of Americans] but to be chosen to play at the highest level for 20 years is a pretty damn good achievement.