I do agree with this in principle but on the other hand, I know people who have had the most dreadfully disadvantaged starts in life and have developed incredible levels of resilience
It is possible for individuals to find a way to crowbar footholds into a better life. Depending on your understanding of a disadvantaged start, I might count as one of them, I certainly meet the op's criteria.
But being able to find those stepping stones is difficult and when you do, they are fickle.
When I was at school a friend and I were living similar shitty lives. We were both smart and were able to go to uni because they were free back in the olden days and we even got a grant. We both moved to London with nothing and did what we could with a lack of resources, money and contacts. We both got married and had children. We both have a chronic illness.
As I write this it sounds like I'm making this up. Disregard it if you like, it is still true.
I'm living far more comfortably than she is simply because the advances in medicine which means that my chronic illness can be controlled and hers cannot. Which means that I am not permanently exhausted, so I can work easily, so I am not dependent on the government, so I can take more risks in things like making small investments and buying property, that have netted benefits, which means that, although we cannot afford private school for our three children we can afford a tutor and my children are doing very well at school. At this point, who knows what is ahead but I am optimistic about my future but my friend is not.