The effective rate actually paid by the top 1% was around 42%, which is not much higher than now: https://taxfoundation.org/taxes-on-the-rich-1950s-not-high/. . The US had also emerged as pretty much the only unbombed industrial country after a global war, giving it a significant advantage.
>so thoroughly debunked by now
Debunked where? Here's a random paper I found showing a strong correlation between economic freedom and GDP: https://mpra.ub.uni-muenchen.de/49220/ . https://www.cato.org/sites/cato.org/files/pubs/efw/efw2019/e... also has a graph on page 18 showing a strong relationship between economic freedom and income per capita.
>What is it with this obsessive focus on supply-side economics, and complete disregard for the demand side?
Demand is a factor in short-term market dislocations, but demand cannot create long-term economic growth. Growth requires that some of the value created be saved and invested, in order to increase capital, and no amount of demand will compensate for a long-term fall in investment.