So I looked up the leaving destinations of my year group (went to a top tier boarding school where my peer group were daughters of a mix of establishment, titles and industry leaders). Over half went to oxbridge and none of those who went to oxbridge studied Medicine. Subject choices were mainly PPE, Maths, Chem eng, natural sciences, history and music. From that group about half went into law and accounting and the other half either went into academia, government management jobs, eng roles or arts areas.
The group that went to RG schools studied everything from law, history, medicine, dentistry, eng lit, economics to pharmacology. Those guys have gone on to work in medical research, technical government roles, started their own business, the arts, media (PR/marketing), IB, accounting and law. While there was one girl who studied computer science she did a law conversion course. Two girls who studied arts courses went on to do a medical degree as a post graduate course.
There were two girls who went to 'ex-polys'. Neither have done well career wise. One has spent 10 years at school and has just qualified as a teacher. IMO it scares me that she is teaching young children as she is quite badly dyslexic and can't spell to save her life. The other girl is a secretary to middle management.
Ironically the girl who left at 16 trained as a hairdresser and IMO is the most successful of the lot of us. She had the academic chops to go to oxbridge but didn't want to go down that path. She has a chain of five successful salons and was a multimillionaire before she turned 30. She employs around 100 people and she loves what she does. That girl was the smartest of all of us.
I think the focus should be on picking a subject area you enjoy and want to explore. However, with the high cost of going to university, you must also consider the financial implications. My good friend has a 1st in English Lit from a RG school. I earn more than double what she earns but she loves her job in the music industry. She is ok with still having student debt 11 years after graduating.