Any effort to prove anything in politics risks being dismissed as post hoc ergo propter hoc. We cannot go back in time, change policy, and measure different results.Until Kennedy dropped the top marginal rates in the first instance of "trickle down" economics.
Unless you can demonstrate the necessary relationship between the cause you claim and the effect you specify, you present a post-hoc fallacy.
What matters is that steeply progressive taxation had beneficial immediate results. Most obviously, it paid down the national debt as a percentage of gross domestic product.