I think that concentrating too much wealth / power into a person’s hands affects their mental health.
I think cause and effect are exactly opposite here: you have to be exceptionally, sociopathically greedy to want to become that rich, and then work towards it. Imagine all the actively harmful and antisocial decisions each billionaire has to make to increase their wealth. I believe most people just aren't cut out for it.
But of course wealth/power then serves as an amplifier.