The point of a progressive tax structure isn't just lower taxes on the poor and "middle class". It's also to incentivize the wealthy to keep their money moving instead of hoarding it. High tax rates on the wealthy and businesses during the mid-20th century are the reason why the US was an economic powerhouse. It forced companies to invest in capital and labor, and therefore report "lower" income and take capital investment tax write-offs, instead of stock buybacks.
How do the wealthy "hoard" money today? It is not like they store piles of copper or warehouses of grain. Maybe having multiple homes they rarely use is a form of hoarding but most wealth is invested in stocks, bonds, and other things that grow the economy. Some heirs of wealth might just be living on yachts spending down their inheritance doing nothing productive but that does not last long.
