@Undercrackers I think that there are a few take aways here.
First, I think that you are right. It is likely slightly harder for the same student to get an admission to a top college coming from a more select high school than from a mediocre high school. (Most likely the explanation is due to colleges wanting diversity. Which I recognize, may be controversial. But, personally, I support.)
Second, your example may not be typical. On average, a student from a more select high school is better prepared for a top college. (That is basically how I interpret the statistics in the paper.)
Third, it is very personal from one student to the next. Yes, your child may have thrived being one of the bigger fish in a smaller pond. For another child this can be very different. Having friends that are more academically interested around oneself can make a big difference for their interests, hobbies, personal habits, etc.
So, I congratulate you on your D and how you raised her. However, that may not be a prescription for everyone.
By the way, I took my younger D out of a top 20 (per US News) high school after sophomore year and put her into a “normal” school (probably similar to your D’s) not because it was hard for her or anything like that. She was doing better than great (straight As, plenty of APs) and seemed very well adjusted. I just wanted her to have more time after school and have a wider circle of friends.
With respect to college, I don’t know if having her change schools was a service or a disservice. For acceptances, it is probably a service, though, I am not sure. With respect to how prepared she is, probably a disservice. With respect to some other softer issues, probably a plus. She does hang out with a different crowd now (I would say that they are more diverse in every sense of the word; more caring; more “real”; but also less motivated academically; don’t often get the more sarcastic humor; …) I think, overall, it was the right decision for her. However, I am definitely not certain.
I guess what I am getting at is that it is not a race for everyone, every child is different, and you may be jumping to conclusions about people’s motivations in this discussion. (Though, to some degree, I suspect you are right with respect to a certain portion of posters.)