Out of billions of people on Earth. If I recall correctly, Toril and most other "generic fantasy worlds" have much smaller populations.It's not even close. Swimming the English Channel isn't even remotely has difficult or impressive as taking on orcus solo and turning him into a baseball bat. A few hundred people make that swim every year these days.
You're taking the metaphor too seriously. Perhaps "D&D characters are the fantasy equivalent of Gold Medalist Olympians" would be more accurate? The point was that D&D Martials should be the physical peak of a magical world's humanoid population. And fantasy worlds allow for more unrealistic athletic capabilities than the real world does.The D&D equivalent would at best be something that a few hundred people from one particular setting could do annually. Even the Forgotten Realms, the setting most heavily dripping with powerful people, could probably only field 3 or 4 capable of that, and maybe 0. I'm not sure that even Elminster or the Simbul could do it solo, and they are the most powerful.