To be clear- the 90% tax rate was a MARGINAL tax rate[1] and doesn't equate to the overall tax rate a wealthy person pays. They might pay 90% on their top 10% of earnings but overall their total tax rate might be 25%

Elimination of the very progressive tax rates and flattening of the tax brackets has increased income inequality as did the lower rate on capital gains.

[1] https://www.investopedia.com/terms/m/marginaltaxrate.asp