If you read the article, they are calculating a fictitious thing they call the “true tax rate”. This is the tax paid compared to the growth in assets.

That is not an income tax. It’s a wealth tax. It feels like conflating the debt and the deficit. Effectively you would have to have a deemed sale of all assets at the end of the year and pay tax on the gain/loss.

I agree that the rich have access to tax planning machinations that most tax payers do not. But this doesn’t bluster their argument.