In terms of nominal GDP per capita, the US is around $85k with Poland at $25k, so US GDP would need to fall around 70%, which would be an unprecedented fall, the kind historically only associated with mass bombing or extreme hyperinflation.
US median income is just over 19 k international dollars, Poland is just under 9 k. Still a big difference but just over a factor of 2 instead of over 3.5.
See https://worldpopulationreview.com/country-rankings/median-in...
In a more homogenous society, such as Poland’s in comparison to the United States, it also in my observation trends to be easier for wealth distribution to flatten.
Maybe the US has more kids per capita too which would also affect that value depending on how it is being measured. Not to say that anything is being hidden there, just something to think about that may make you interpret the data differently or think about it differently.