But the second half of the 20th century was mostly a victory for the low-tax side. [...]
Politicians cut every tax that fell heavily on the wealthy: high-end income taxes, investment taxes, the estate tax and the corporate tax.
The justification for doing so was usually that the economy as a whole would benefit.

The justification turned out to be wrong.
The wealthy, and only the wealthy, have done fantastically well over the last several decades.