It is better for the United States to look at Indian Tax structures and codes. Because that’s this country’s future. You can’t have a thin section of tax payers supporting the majority of the population.
Developed vs developing countries is not just about standard of living. It is about GDP and what percentage of the population is productive. By that measure, America is a developing country.
https://en.m.wikipedia.org/wiki/Developing_country A developing country is a country with a less developed industrial base and a low Human Development Index (HDI) relative to other countries.[1] However, this definition is not universally agreed upon. There is also no clear agreement on which countries fit this category.[2][3] The term low and middle-income country (LMIC) is often used interchangeably but refers only to the economy of the countries. The World Bank classifies the world's economies into four groups, based on Gross National Income per capita: high, upper-middle, lower-middle, and low income countries. Least developed countries, landlocked developing countries and small island developing states are all sub-groupings of developing countries. Countries on the other end of the spectrum are usually referred to as high-income countries or developed countries.
That is a 5% tax estimate on total wealth, if you take the percentage of actual wealth increase then it is much higher.
To be honest a fixed percentage tax would then be better because it will force them to invest, too big percentage and they will have to take risky investments, and forcing people in that corner is not good.