This seems a lot until you notice that really rich people don't pay these taxes. They make capital gains or receive dividends, which are either tax free or taxed at a much advantaged rate. This is why there is such a great separation between the 1% and the rest of the population.
The article specifically states that the OECD analysis estimated 'payroll taxes, federal income tax, state and local government taxes.'
"Excluded are the countless other ways that governments levy taxes, such as sales and value-added taxes, property taxes, and taxes on investment income and gains."
They also don't include self-employment tax (15%) and sales tax (6-10%). Sales tax and self-employment alone are over 20% close to 25% not counted in the article. Property tax can be close to 1% (depends on property), dividend taxes also aren't included (10-15%).
There are lots of taxes beyond income tax. Basically taxes take about .35-.50 out of every dollar earned through income, sales, other taxes. Business expenses for businesses, kids, credits and other things can help bring it down as well as standard deductions but it is still high.