No one asks to be born into the Royal Family. It must be difficult as a child growing up knowing that you are always second best to your sibling and that the attention is always on them. It doesn't matter how much wealth you have, you can still have mental health problems, suffer from low self worth
I don't disagree, but mental health issues affect the majority of people at some point in their lives. I believe the statistic is that, at any one time, one in four people is suffering from a mental health issue.
However, the vast majority of people have to struggle to keep going in day to day life. For the average person on the street, developing a mental health issue means joining a 2 year waiting list for any kind of therapy on the NHS, while in the meantime having to carry on with work, keeping your household going, looking after your family etc.
If you are wealthy enough not to have to work and to be able to afford immediate private medical help, of course that doesn't immediately take the mental health problem away, but you are in a far better position than someone who is forced to just get on with things, or who has a breakdown and ends up in debt or even homeless.
I say again, if the Royal Family really cared about the mental health of their 'subjects' they wouldn't sit on vast piles of wealth and property - they'd make them available for those who are most in need in society, and just maintain one house each (which even then would be vastly larger and more luxurious than anyone should have a right to expect without having worked for it).