This result is robust to inclusion of realities such as differing skill among entrepreneurs.

The key thing is that this paper looks at generational wealth accumulation. Even if families which consistently churn out stellar business people were in any way common (data says otherwise) that effect is still completely overwritten by already being ahead. As a billionaire kid, the extent of business skill you need to have to not lose everything is to hire people who have business skill and then slurp Caipirinhas on your yacht from your ample, ample dividends. And if you lose everything, well, you're losing it, on aggregate, to other billionaires, so wealth concentration still proceeds.