Two kids who both went to the same school, were told the same things about the importance of the SAT and dedicated equal time to study and preparation can probably say that the difference in their scores is indicative of differences in intelligence.
But any two random students? There are so many factors that could cause students to underperform their hypothetical max score if they had perfect conditions in the months leading up to the test and day of.
I don't understand the effort to try to eliminate the reality that innate ability exists. I think we should accept this and work to cultivate it. Just because somebody of average aptitude doesn't mean he might not excel in other ways. The world needs all sorts of people, and I think the ideal system would work to figure out and cultivate these talents in everybody.
I never studied for tests in school, not for the SATs, either. I tried that in college, that did not work. The stress of the tests was pretty bad. I realized I had to study hard, and I did, and it was effective at reducing test anxiety.