I'm getting lost. Surely the point is that some children have more social capital and thus better access to informed advice. DH is an economist and DS is studying economics. It is natural for them to discuss options, content, who is teaching and so on. DS will make his own decisions but welcomes input. He is lucky he has an uncle who is a lawyer and one who is an engineer and so had he been studying a different subject he might well have had similar discussions with one of them. The type of school is part of this but not the only part.
There are some generous posters: Molio, Hayita and AlreadyTaken to name but three, who are willing to share their experience and knowledge. Indeed I am particuarly grateful to AlreadyTaken for helping steer me, and thus by extention DD, through the maze of Medical School applications. If "which Oxford College" is a legitimate question, which medical school is more so. No one is right all the time, but there are plenty whose views are worth hearing. The kneejerk response of "stealth boasting" or something about the inequity of state/private is tedious. Higher Education is a huge investment decision and kids have varying degrees of access to good advice. MN is not perfect but is another source of information.
I also think Littleham, upthread was right. It really depends on the child. Some need more help than others, for a variety of reasons. Yes, I never saw DS' PS. DD was very ill last summer so getting a UCAS application in by the October deadline was a real struggle. DC grow up pretty fast during Yr 13 and the first year of University. But some faster than others. With some really struggling and needing support from both home and school/University. There is no firm rule, but a case of trying to find the right balance.
FWIW I think Hayita is probably right in terms of her advice to OP about Natural Sciences. We certainly picked up similar when looking at Plan Bs for would be medic DD. And I am pretty sure that Hayita's points about Financial Maths are correct as well. DS's degree is overwhelmingly Financial Maths, yet he would not claim to be a mathematician.