I think OP's point is that due to the complexity of tax laws, especially for the wealthy who have more non-wage income, the tax rate doesn't capture as useful a picture as actual dollars of taxes paid.

There's your tax bracket and then there's what you actually pay after deductions, loopholes, etc.

The common argument is that the 70% rate of the 1950's was never actually paid by anybody and the effective tax rate was much lower. By looking at actual taxes paid that entire argument can be skipped.

Anybody who studies historical taxes professionally should know this, so when they use a worse measure it looks like they're doing so because it fits their narrative.