> The USSR didn’t actually have economic equality.

More or less it had. Except for privileged commie bosses everyone poor. "Rich" had cars (!) Having noticeable business was prohibited. Selling own potatoes on flea market, or growing chicken and pigs was fine.

> The US has drastically lower tax rates for capital gains.

In Mass. it's 10% to begin with.

> I’m saying economic growth is slowed through the economic inefficiency resulting from unequal taxation.

Not sure about this. Do you have examples when equal taxation helps?