I do understand the initial example; and I have a story similar to yours. But you're comparing apples to oranges here: the experience of having a decent working memory and getting good grades due to schools being unable to test for real knowledge (but regurgitation of facts) and catering to the lowest common denominator, vs the ability to play a musical instrument skillfully are two very, very different problems.

My claim is that the latter is a skill that nobody is born with. Autistic savants aren't some type of magic creature that know things just by virtue of being savants. They still have to go through the process of skill acquisition. Now that process may be accelerated compared to me or you, but I disagree with your claim of proficiency with zero effort, especially with skills that have shown to require thousands of hours of deliberate practice to establish proficiency.

I think the key is in your last statement: "or appeared effortless relative to peers' efforts". It seems you found yourself in an environment which didn't sufficiently challenge you. This would only argue that you should've been pushed up to more challenging AP/honors classes. This would again have the effect of placing you in a higher standing compared to your peers. So if both you and your peers would be pushed to your true potential, it seems consistent with your statements to say your performance/output would've been superior.

So why should colleges deny you entry because of your ability to be proficient in the system they've set up?