I haven’t read the full thread OP, but I’ve read your posts, and I think maybe what you might be missing is the rather intangible but ever present elitism in the UK that underpins a lot of our systems, the choices we make, and where we get to in life.
The system in the country you’re from sounds like it’s based on merit. You work hard and do well = qualifications & experience = good job.
It’s not like that here in the UK - we like to pretend it is, and it sort of it to a limited to extend, but the truth is that there are many many other factors at play.
When you start reading about universities, you will hear people talk about ‘prestige’ and be keen to get into the most prestigious universities. That’s your Oxbridge, your Durham, St Andrews etc. These universities are very good, but the prestige isn’t ONLY because they are very good. It’s because they are traditionally upper class universities. They are ancient, have influential alumni, attract lots of funding, international reputation, so they attract the brightest and the best, are very competitive to get into, consequently produce world leading academics - etc. It’s self perpetuating. So it’s good to go to Oxbridge, but not because of the teaching per se. You will get equally good teaching (if not better) in many other universities (look for the Teaching ratings) but what’s different about oxbridge and ‘prestigious’ universities is that you are being taught by, and alongside, people with influence. People with reputation, or talent, or networks, or money, and meny combination thereof.
So, when you graduate from a prestigious university with a 2:2 you won’t necessarily be better at Physics than somebody who got a 1st from an ex-polytechnic, but you will have a million more opportunities because of the people you know, networks that are open to you, and because of the respected name of that university on your CV.
So, prestigious universities are important if you want to be successful and influential in the corporate world, in law, in politics, in business. For careers that carry power, influence, and money ... get yourself into a “prestigious” (old) university. To find them, look at the proportion of private school pupils who go there, and at their famous alumni.
You will also read about Russell Group universities. These pride themselves on the quality of their research. They carry less “prestige” (in social terms) than the likes of Oxbridge, but they are very respectable universities and employers who care about the academic rigour of their new recruits will like to see a Russell Group university. If you want to have a career in academia or science, technology or medicine, then Russell Group universities are a good choice. They have high entry requirements so you need to work hard to get in. Because of their focus on research, Russell group universities tend to be well funded and have good facilities. They will have extensive libraries and staff who are passionate about their subjects. Sometimes the teaching suffers a little (I am generalising here of course) because of the focus on staff’s own research output, so look for a good teaching rating for your chosen subject in a Russell Group university.
Then there’s the ‘other’ universities. Many are truly excellent, some are awful. In my opinion, this is where it’s most important to pay attention to things like staff:student ratio etc, and visit to get a feel for the university.
Goingn to a university that is neither prestigious or Russell Group will put you at a disadvantage if you want to become a partner in a Magic Circle firm or the next Prime Minister. But if you want to become a solicitor, a teacher, a dentist, an engineer, an accountant, these careers are still open to you if you have good grades.
In my humble opinion, there is a lot to be said for going to a non-Russell Group university in a city you love, where you can do the hobbies you enjoy and meet “your” people. You will get good quality teaching (check the standards) by lecturers who are prioritising your education, not their own research output. You are less likely to feel the pressure of working alongside / competing with the student who got 15 A*/9s at A Level, or be too afraid of asking ‘stupid questions’ to the professor whonis the buggest name in the business. With a 1st or 2:1 at any university you can go on to further study or a professional career and lead a very happy and successful life as a fully rounded person who also enjoyed their university experience. A school I know has two teachers in Year 1. One went to St Andrews, one went to literally the worst university in the local area. They were employed based on how well they taught a lesson at interview. They are both excellent teachers and both are paid the same salary. Sometimes it just doesn’t matter.
As for the subject =/= job thing... basically, you can do a further degree (often a Masters, sometimes a diploma, sometimes other qualifications) to ‘convert’ to another discipline if you have a particular profession in mind. Law, medicine, journalism, psychology... probably loads of others... you can’t go straight in with a History degree, but with an additional top up course/degree, you can still qualify as a lawyer (for example). So very few careers are closed off to you, as long as tou don’t mind firther study.
On the other hand, if your heart is set on being a botanist (or a historian) it makes sense to do the subject and see what opportunities open up for you. It’s wonderful to do what you love for a job.
Anyway this monster post has gone on long enough, I hope it wasn’t too boring /patronising and that it was useful.