To be more correct, it’s a 7% decrease in income over $5,000,000 (if the total tax rate on that income was 50% before and went to 53.5%, the amount remaining dropped by 7%).
I think this point is under-appreciated. As the top federal tax rate has dropped over the decades, each additional percentage point drop has given less proportional value to top-rate-payers, while costing proportionally more of remaining federal revenue. In that sense, the lower the tax rate already is, the more expensive a tax cut is to the government. The higher the tax rate already is, the more expensive a tax increase is to taxpayers.
This is why tax cuts under Bush and Trump blew up the federal budget - tax rates were already pretty low, so quite deep cuts to revenue were required to deliver any notable benefit to high-rate taxpayers. It’s hard to make rich people much richer by cutting taxes when they are already keeping most of their income. In the case of the Trump tax cut, rates were already so low it required raising taxes on some to cut for others.
On the other hand, you can go back and find times when after-tax income of top rate payers doubled because the top rate dropped from eg. 91% to 77%, which delivered a lot of relative value to those taxpayers while fitting more easily into the federal budget (although as always, it’s probably more complicated as tax bills make changes to deductions when they change rates).