BS accepting reclassed 9th over 8th gr?

My question wasn’t should a kid reclass to get an edge, and what am I missing.
It would be irresponsible to hold a kid back who is ready just to get into any school. And I totally get those that reclass for age, maturity, concerns about boarding young, transferring etc.

It was wouldn’t admissions consider *
most reclassed students stronger candidates in the pool, and what am I missing.

From others responses here and elsewhere on his forum, I gather most people really don’t think there’s much direct comparison and that despite the extra year of high school level academics if 9-9, they don’t think it factors in on the 1:1 student level during admissions. Though I was surprised to hear that, anecdotally 15-40% of some classes are reclassed students. I’m not sure how accurate this. Thank you