I think the "86% of billionaires" thing can be attributed to wealth concentration to income gap. If you want to be a billionaire, it helps if your family had many millions. The extraction of the ultra wealthy that has happened in the last 40 years is pretty incredible. I'm unsure that there are any billionaires that started out leaving home as an emancipated minor with no job and no money an an early life of untreated trauma resulting in complex PTSD.