The SATs have been re-centered several times. When I was applying to colleges, before the '80s, only two schools in the country had median scores above the 1300s. Scores in the 1300s were highly competitive basically everywhere.
When we lived in Manhattan, a kid getting into Hunter elementary was like winning the lottery. Because people were concerned about the education quality in the public schools prior to HS. Getting into Hunter meant they didn’t have to pay huge private school tuition bills, or move to the suburbs.
I am acquainted with several alums of its high school, and I have never witnessed a more talented and accomplished group of people. It is, or at least was, truly a remarkable school.
As a freshman in college I did a project with two grads of Bronx Science. They were clearly much better prepared than I was.
As for getting into college, I too have heard that it may actually be a disadvantage. Aside from the top boarding school anecdotes, I know several residents of Scarsdale who feel that their kids are actually disadvantaged. It could particularly be an issue if the school is large, because few colleges want to fill their class entirely with qualified students from just one school.
On the other hand, it may not be altogether a disadvantage. This is going into the wayback machine, but back when I was applying , I knew the valedictorian of a small non-elite private school , who applied to Yale and was denied. The guidance counselor followed up, and he was told , to the effect of, “if we take him that would mean denying a kid from (elite feeder school that was down the street)”. Of course this only speaks to how that one university handled things a very long time ago. But it implies that “elite feeder” was helpful to get the students “in the game” for that university. But maybe the university did not go deep into the ranks of that elite feeder school to admit all of its deserving applicants.
But regardless of advantages or disadvantages for college admissions, I believe it is clearly beneficial in the long run, in providing the skills that promote life achievement. Beyond college admissions. College is just one step in the rung, not the end game.