You're implicitly modeling difficulty as a single number, and ability as another single number that determines the maximum difficulty of the problems you can solve.

However, according to Feynman, you can sometimes solve problems that smarter people can't by having "a different box of tools". The quote:

That book also showed how to differentiate parameters under the integral sign - it's a certain operation. It turns out that's not taught very much in the universities; they don't emphasize it. But I caught on how to use that method, and I used that one damn tool again and again. So because I was self-taught using that book, I had peculiar methods of doing integrals.

The result was, when guys at MIT or Princeton had trouble doing a certain integral, it was because they couldn't do it with the standard methods they had learned in school. If it was contour integration, they would have found it; if it was a simple series expansion, they would have found it. Then I come along and try differentiating under the integral sign, and often it worked. So I got a great reputation for doing integrals, only because my box of tools was different from everybody else's, and they had tried all their tools on it before giving the problem to me.

I don't think this changes the picture very much, though. You just divide the people in the field according to their box of tools. Pick the group with the box of tools that can solve the problem, and your model applies to them.