"middle class" that's bearing the burden. It's the high earners that go to work every day, and don't feel particularly rich, but really are, that bear the burden. The tax code starts to really take a bite in the $200K+ range. That's not middle class in any sense, but it's also very different from someone with a net worth of $100 million.

I also think you'd be hard pressed to find an effective rate (against income) of the super wealthy in the sub-14% range. I don't know how you even get there since the lowest tax rate someone in that bracket would be subject to is 20% LTCG + 3.8% ACA. I suppose if you want to say that a billionaire with $50 million in investment income who gives $25 million to charity is only paying an 11.9% effective rate since he reduces his investment income in half, you can get there, but I don't think you should count charitable deductions as a reduction to one's effective tax rate. They're giving the money away so it comes out of both the numerator (taxes paid) and denominator (income).

In addition, the IRS publishes pretty detailed tax stats by AGI bracket. For 2017, there were 20k returns with AGI of $10 million or more with an aggregate AGI of $635 billion and taxable income of $542 billion. Totally income tax was $159 billion... so 29% of taxable income, and 24% of AGI. Now that tax may be a really small % of their net worth, but it's not an insignificant portion of realized income.