The overall tax burden is relatively flat

[opebo]

Of course, whether it makes sense to count Social Security and Medicare payroll taxes the same as income taxes in assessing the progressivity of the tax code is open to debate.  Nominally, you're paying into a retirement program.  The reason why the payroll taxes are capped at income of $110,000 is because the benefits one is eligible to draw upon retirement are basically the same for everyone.

What if you computed the progressivity with income of taxes paid into the government minus benefits received from the government?

Well, the problem there is, Mordant, that the right-wing is apparently unwilling to admit that the vast incomes of the wealthy are benefits received from the government.

[opebo]

While I wouldn't go as far as opebo, if you're going to start deducting the benefits received from the government, to be equitable you'd need to dedcut things such as the value of corporate limited liability, corporate welfare, etc., that at the individual level primarily benefit the rich, but which are harder to quantify than direct assistance.

All incomes are created by society as organized by the State, and distributed by the State.