There's also the basic observation that many big companies that provide valuable products and services pay rich people lots of money to run them or compensate them for their financial help. Would there be an Uber at all without anyone getting rich off it?
Another observation - when we need a doctor or a lawyer, we find their contributions to us to be worth so much we'll pay them more than we pay a cleaner. After all, we could do the cleaning ourselves if we had to but the barrier to start operating on ourselves or writing our own contracts is higher and those rich people have invested work in overcoming that barrier so they could provide those services to people who can't.
Isn't that basically what you'd expect with a progressive tax system? Paying taxes is not the only way to contribute to society -- almost all the money people earn do to some extent, through taxes, and consumption, and investments, etc. Which contributes more I don't know. That's why I was hoping for a citation.
To your second point, there is evidence that CEO performance is negatively related to their pay: http://papers.ssrn.com/sol3/papers.cfm?abstract_id=1572085. Measuring competence is difficult, wealth is a appealing proxy but maybe not that reliable.
