Things I don't understand about Oxbridge

Since you’re talking about HYPSM, this is absolutely false. These colleges are need blind. They want to recruit the best students in the world and they have enough endowment to make them attend regardless of how much they have to pay in financial aid. They don’t even need to offer merit aid - if you can afford the school and got in, your choice, and evidently there’s no shortage of families who think it’s a worthy use of their hard earned money; if you can’t afford the school, they’ll provide you with amazing financial aid, so that if you’re working class or poor they’ll cover tuition, fees, room board, transportation, books, and you may even end up with a stipend. Most Top 20 universities and LACs will offer excellent financial aid packages to domestic applicants, with families generally paying less than they would at a state university. There, a family of 4 that makes 65k or less is not expected to contribute ANYTHING and everything is scholarships and grants, not loans. You qualify for serious financial aid up to 180k a year.
Contributions, even from alumni, have to number in the millions to matter (and the kid has to be at least marginally qualified - same thing as with nobility/royals in the UK, they can’t be totally unqualified… note that with privilege come enough tutors, good schools, etc, that it shouldn’t be that hard.) General contributions can’t “get you in” at all, as alumni find out every year.

What I implied about US admission to top medical schools is correct. It isn’t like in Britain, where they are looking at a bunch of high school students with A*s on A-levels. It is possible to get a score on the MCAT that puts you in the top 10 or so in the country. You can also get close to all As at a top college. So you can put together an academic record that will almost certainly get you in. Of course they look at the interview, essays, and so on.

However, it isn’t just a few people with high class connections. Doctors use money to get their kids into the right college, medical school, residency, and so on, trying to get them into a lucrative specialty and/or a practice in a wealthy area. This does account for a large percentage of the students at top medical schools, and it is probably similar for top law and MBA schools.

A*'s and A’s are heavily concentrated in private schools (which cater to a specific social group and are even less socio-economically diverse than top boarding schools in the US) and in upper-middle class schools.
I’m not sure what you’re trying to say?

Note that you cannot “transfer” a UK medical degree to the US. Huge hoops to go through. And vice versa.

As for Laura Spence, the issue is that Harvard practices “holistic” admissions and Oxbridge doesn’t. There are also few places for medicine in the UK, whereas she was simply admitted to the freshman year at Harvard.

One thing Laura did note is that after graduating from Harvard, she “breezed” into a British medical course.

Note that Laura got a full scholarship to Harvard on the basis of financial need.