I think it is a pretty widely shared consensus in economics that "the American Dream" was the truest in the beginning of the 20th century, when European regimes

I think it is a pretty widely shared consensus in economics that "the American Dream" was the truest in the beginning of the 20th century, when European regimes were aristocracies and peasants were regularly starving to death. That was why waves of immigrants arrived from Europe to the US. After WWII the situation basically got reversed: Europe experienced such a shock and disruption to the existing social order/redistribution of wealth etc., that it went really left-wing/"social democratic". In the meantime, the US saw a greater and greater concentration of wealth and the division between the rich and the poor got increasingly stark, and social mobility is much worse than that in, say, Northern Europe. The American Dream as people knew it is pretty much dead. This is also one huge reason behind the polarization in politics that we see nowadays. Unfortunately, a lot of narratives in the US don't seem to realize/willingly ignore this situation and still seem to talk about the old idea of "bootstrapping" and American exceptionalism in this regard, which is really kinda one century out of date already.