This is correct. Piketty's research has shown that as one moves to progressively higher echelons of the wealth distribution (top 5%, top 0.1%, top 0.01%), a higher and higher proportion of capital is accumulated through returns on capital rather than income. That being said, we shouldn't discount that while taxes on income are more progressive than taxes on wealth, they're still significantly less progressive than those of most other Western countries (and we have significantly higher levels of income inequality compared to those countries.)