I just thought what the root post was implying is that even if you're passionate, you might not have the potential to achieve genius-level skill because that would somehow be genetically predetermined. If that was what he was implying, I'd love to see some evidence to support the claim.
But more - it's the only reasonable-sounding argument for that part of the "Myth of a Meritocracy".
The caveat for the real argument is: People are more complicated than animals, and there's way more to it than genetics.
The real argument is: If everyone was capable of everything, evolution wouldn't work as a process.
The addendum of: of course this is inaccurate, poorly phrase, etc etc - the idea is still "new" enough to be unpolished.
Thoughts?
Quite on the contrary, I've seen plenty of evidence to suggest that genius is at all not genetic, and that you can train children to become prodigies, and later, geniuses. Surely you've heard of Judit Polgár, universally considered the best female chess player of all time? She was made a genius, not born. Her two sisters grown to become Grandmasters as well. And here's Dr. Frankenstein: https://en.wikipedia.org/wiki/László_Polgár
The article also never claims that everyone IS a mathematical genius, only that they have the potential to become geniuses. Whether or not the achieve this potential in their lifetimes is another matter entirely that doesn't contradict what your quote implies (that only a small percent of the population can be among the "best" at any given time, by definition).