At least in theory, the SAT should help adjust and give us a sense of the pool. If you use 1500+ as a demarcation line, there are ~21,000 kids annually that achieve this score. SAT is obviously far from the only factor, but assuming 90-95% of this population also are top academic performers (think top 5-10% of class) you get ~19,000 kids.
Ultimately getting into Duke specifically for anyone is challenging. You just have to hope at this point that by “shot-gunning” to the top schools, you will make it into at least 1 (which of course, is the max you can actually attend).
Note for reference, there are ~20,000 undergrad spots per class in the Ivy+Stanford+MIT+Duke+Chicago. Counting other top schools like Georgetown, Hopkins, NW, Vandy, ND, etc. plus the liberal arts schools, my hope for top performing kids today (at least based on standardized tests) is that everyone in this range will have at least 1 option if the kid wants to pursue that route (not all do). Thats my hope at least for the youth of today