As a TA, I've seen adults try to pass initial college calculus many times (and failing - you were allowed to try several times) with enormous effort. It's not a small multiplier

And this was still people selected from the small subset of the population choosing an engineering major. Human are much, much more different than you seem to think

There are many, many people (math majors, competitive programmers, chess players, etc) who devote incredible effort to becoming better, and simply cannot reach elite levels. And while in most cases elite players are also putting in a lot of effort, there are many cases where it is still relatively less than their peers who are trying harder but still lagging them.

Would you ever be tempted to make such a claim (that everyone is close to the same in ability and effort is the main determiner of success) about athletes? It's so obviously untrue that it's laughable. Why would you think that mental ability is magically distributed evenly?

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