I think if we turn it back-to-front, and say that there is a massive disadvantage in not having supportive parents, then that might make more sense. My friend went to posh public school, but her dad was an alcoholic and her mum not very nice, and when it came to university, her dad was having a three-year black out and refused to fill out forms or help in any way, and the mum had no idea about finances or paperwork and it was in the late 80s when grants were 'means tested' - this meant you had to get your parents to fill out the forms and if they wouldn't, you had to wait 3 years in order to qualify for a grant for yourself (not like today when you can get a student loan for yourself and go even if your parents don't want you to). So she didn't go.
I didn't go either, because either I wasn't clever enough to get the grades, or my local state school didn't push me hard enough... However, my parents bought me my first car, which saved me about £1000, but my friend had to save up for hers. My parents also helped me out with the deposit for my house, but my friend had to save up for hers.
I now live in a much bigger house than her and have always been better off. I married a man who had a well-paid job, so never had to work and she did not, and has worked in admin jobs since she was 18.
I am not a better person than her, and she is not a better person than me, but I have done better in life. She has terrible anxiety and is socially very cautious whereas I am much more outgoing and just generally happier.
Her parents are still very well-off - big house in the country, second home in the South of France, but they don't help at all.