The term "supernatural" is unhelpful in a context where magic is ubiquitous.
The term "supernatural" is a scientific concept. Science establishes the "laws" by which the universe functions. Supernatural is something beyond the universe that can interfere with and override the laws of the universe.
The only time the term supernatural might make sense in D&D is if it specifically refers to the Astral Plane with its Celestials, Fiends, Clerics and Paladins, who are "beyond" the Material Plane.
I am really not trying to go down a rabbit hole here and so don't need a response. But I'm trying to work this out in my head for my own uses in the future - so feel free to give one if you think it would help. (Thanks either way!)
I hope my comment helps sort the terms.
Everyone in the world clearly doesn't have the potential to dunk a basketball at regulation height without assistance. Does requiring height make it extraordinary?
Height correlates with DNA, but culture and events can significantly alter someones height.
Normal reallife humans include heights that roughly correspond to D&D Large (over 8 foot) and Small (under 4 foot).
So, Large and Small sizes are "ordinary".
However, for a human or humanshape to be Huge and Tiny seems extraordinary to me.
Not everyone who wants to can hit a professionally thrown fastball with any noticeable chance (even great athletes from other sports). etc...
Actually, sports and weighttraining and so on, very much are learned skills.
A person might have an innate talent for certain skills, but learning and experience still matter.
So, ordinary.
Is it different if in the world it takes a certain amount of Ki to call upon it in a way that's large enough to get a game effect from it? When would it pass from extraordinary to supernatural according to the base laws of the world?
Ki is natural. Every human, every animal, indeed everything, and the cosmos, exhibits ki.
It is possible to talk about ordinary uses of ki, versus extraordinary uses of ki.
If you're in a world that widely accepts magic (Dying Earth, Lord Darcy, Garrett Files, etc...), is magic considered "supernatural" still?
If the world itself is magical, then magic is natural.
If the world itself is void of magic, but magic from beyond the world can override it, then this otherworldly source of magic would be supernatural.
Are mutants in the 616 extraordinary or supernatural? Hawkeye?
Mutant superheroes are natural, magic, and extraordinary.
If Hawkeye is an olympic level athlete and sharphooter, who uses hi-tech, then he would be natural and extraordinary.