You're assuming there is a meaningful notion of maths ability that's independent of effort. I don't believe this. How could you possibly define, let alone measure, such a thing?
But this idea applies to literally everything (you can't measure ability to learn a language until you measure what a student can learn after a certain amount of effort). Yet we still have ways of estimating ability. IQ is one of them.
Actually, now that I thInk about it, brain scans may be starting to reveal some of this kind of information.
