The USSR didn’t actually have economic equality.
The US has drastically lower tax rates for capital gains.
Finally, arguing for equal taxation isn’t arguing for equal pay.
As to my actual argument, I’m saying economic growth is slowed through the economic inefficiency resulting from unequal taxation. The point of economics is to make goods and services people want and capitalism achieves this through investments and exchanges of money. But distorting that feedback loop through taxes unequal taxes on individuals or companies is a distortion. Invest in the wrong things and economic growth stalls.