I'm kind of astonished that you think this, there are lots of studies about intergenerational economic mobility in the USA compared to other places.

https://www.chicagofed.org/research/content-areas/mobility/i... for instance.

https://www.mdpi.com/1660-4601/17/4/1179

Anecdotally, I can also attest to it. I know lots of "finally successful" folks who end up spending their wealth keeping their siblings and extended family afloat. There's no real safety net for them in the USA.