I don't think doctors and nurses running from Britain to save the US is a thing. The brain drain of med professionals to the UK and the US is due to the money, and also because many doctors and nurses in developing countries despair when faced with the bricks without straw daily grind of their professional lives, seeing patients die whom they know they could help if only they had facilities or supplies or even clean running water. Britain, Canada, Australia and especially the US are destinations for migrating doctors from less developed parts of the world. They often end up practicing in areas of the US where American doctors, saddled with huge med school debts, can't afford to practice, or in specialties that American med school doctors tend not to study (general practice) because they will not be able to pay off their med school loans on the sort of salary a GP makes.
the "graduate" status of your medical degree is there because the basic education that people enter with isn't of a high enough level to go straight in, hence they get a college degree first.
This is not really the case. Medical degrees and law degrees are graduate degrees in the US because undergraduate education and professional education there are conceived of as separate undertakings, and seen differently to how they are conceived of in the UK (and Ireland). The liberal arts and sciences model holds sway in the US. A well rounded and versatile graduate is expected as the product of an American undergrad degree course. She is expected to have mastered a foreign language or two, advanced mathematics, lab sciences, humanities history, philosophy, economics, etc as well as English, on top of her major. Back in my exFIL's day, Latin and Greek were expected.
In the UK, undergrad degrees tend to take less time and are more specialised. The UK secondary system allows (or forces) early specialisation and it is arguable that as a result there are many unhappy square pegs in round holes, engineers who can't put a sentence together, English grads whose knowledge of maths or economics or lab sciences is dodgy, etc. You get a situation where a Classics grad from Oxford who dropped maths after GCSE and never studied economics or finance gets a job in the Treasury that she will most likely hold for her entire working life, with goodness knows how much impact.
I actually don't see an advantage to the early specialisation in the UK. (Ireland escapes that with the Leaving Cert. Perhaps that is why the IB isn't so big in Ireland -- one primary years, one middle years and one diploma school in the Republic).
It really is a case of apples and oranges. Imo the big advantage of the American system is versatility of graduates, which makes a difference as economies develop and change especially in a technological sense, and as well as that a well rounded graduate class is an advantage to a democracy. A common language of sorts is spoken. It is worth noting that the military academies also feature a liberal arts education.
It is not only the spectacularly advantaged or the anomalies in the US who perform really well. In the last three years, students from the local high school have gone to St Andrews and Edinburgh. DD1 was placed in Calc III in university and iirc took another semester of mathematics beyond that, doing lord knows what. She did BC calc in high school (an AP course) having started at exactly the level of maths I was doing in Ireland at the age she started high school. BC calc was the terminus of the bog standard bright kid track in maths in the school. She tested out of French in university, having done honours French in high school, not AP. She nevertheless took a year of French in university and did a semester abroad in Paris. Her AP coursework in general gave her a legup. AP level courses are not just available to an elite. DS and DD2 had similar trajectories, except DS did Latin in HS and took German in university. DD2 will be heading to UCL next semester and I anticipate she will hit the ground running just as her classmates will if they go abroad.