If we go back to Buffett's original please-tax-me-more discussion, which I just found again after losing it, he made the argument in a 2007 interview:
The billionaire investor took his pro-estate tax campaign to Capitol Hill.
www.forbes.com
So Buffett has a small army of CPAs and attorneys formulating his tax strategy, pays himself low wages, makes the majority of his ~$50M dollar income from capital gains and dividends, and then compares his net federal tax rate of 18% to his average office rate of - wait for it - 33%. That was quite a well-compensated office staff for 2007 in Omaha. So... using the 2006 married filing jointly tax tables, here:
It looks like to get a net rate of 33% you'd probably need a household income of about $400-500K per year in wages, depending on income and deduction factors (which were a lot better then than they are now). Not bad at all. And, as I pointed out earlier, Buffett pays himself only $100K per year, even then. So please-tax-me-more Warren seems to be complaining about how his taxes are low, but obviously uses his tax management army wisely.
Given how much he's been giving away lately it wouldn't shock me to find his 2020 tax rate to be in the single digits percent.
I think billionaires should stop whining about their embarrassingly low tax rates, and if they feel guilty about it just mail the treasury a donation every year (the address is in the Form 1040 instructions). I'm not a big Buffett fan. He works the system for every dime possible, and then complains because the laws allow it. And then he hides his estate in the Gates Foundation to escape estate taxes. Nope, not a big fan.