I've been thinking a little about that example. And I really don't think it gets at the core of the issue. The problem with that example is that academic disciplines, whether it's due to an inferiority complex or what, have decided to model themselves so much after the hard sciences, so that of course the hard science experts are going to be able to study any of those disciplines and acquire a PhD. It's because the programs were modeled after the hard sciences.
Take a different example: if aliens came to earth and demanded that all PhD physicists get as good at sculpting, drawing, and designing as the world's foremost artists; and all the artists must acquire PhD's in physics. I'm not sure who would do better as there's not a clear hierarchy between the disciplines. They're different fields, catering to people with different interests and talents.
Indeed, among the physicists we might also find those who are moved to tears by Baudelaire, and among the critics of French literature those unafraid of contour integrals.
For every Terence Tao there are a thousand Nameless Toilers. So intelligence, for most people, is not a rocket to ride but a bar to clear.
Then, given enough of a brain to be taught, the more important question: do you have the stomach to learn?
I'm not sure sculpting/drawing are the best examples. You can't learn them by memorizing information, you need the motor skills as well. I'm sure they'd do well at designing to the extent that it can be learned from books.
The extreme example would be Mozart and Gauss. I don't think either one could have become one another, even though both of them possessed one-in-billion IQs.
Take a different example: if aliens came to earth and demanded that all PhD physicists get as good at sculpting, drawing, and designing as the world's foremost artists; and all the artists must acquire PhD's in physics. I'm not sure who would do better as there's not a clear hierarchy between the disciplines. They're different fields, catering to people with different interests and talents.