I think it's reasonable to assume that the increased competitiveness in admissions leads to increasingly competitive attempts to game the admissions process.
Whether or not the original claim is true, I think it's certainly true that an increasing amount of cost and effort has gone into SAT prep. Certainly, that was my experience (if we're comparing anecdotes). Everyone I knew in the top percentile of my HS prepped for the SAT, and that was in the early 2000s. Based on one of your other comments, it seems that your personal experience was in the 70s -- how reflective do you think that is of the admissions process today?
The college students I know today didn't prep for it, either, and one was accepted by Stanford and Caltech.
I've seen some claims that the SATs have been "dumbed down" or "re-normed" since the 70s. Certainly, the number of students who apply to elite colleges has increased substantially, which means there will be more with perfect scores.
https://www.compassprep.com/great-to-good-the-diluted-value-...
My scores where good enough to get in almost anywhere in the 2000s, but they're barley above the 50th percentile at our flagship state university now.
It's unlikely that the average intelligence of high schoolers has increased that much. It's much more likely that people have figured out how to prepare for the SAT.
The math needed to ace the SAT is taught in high school. If you slide by on that, you'll probably need a math tutor to make up for it. Or you can choose to learn the math presented in high school.
I've heard that claim a lot, but never accompanied by evidence.
Nobody I knew prepped for the SAT, and many got into top schools. Unless you count paying attention in math class, and reading adult level books "prepping".