This is untrue.

Here is a measure of upward mobility. We are 27 out of 82 right below Lithuania

https://en.wikipedia.org/wiki/Global_Social_Mobility_Index

That index measures a lot of things, most of which aren't related to the probability of a random person becoming rich.

However, despite the fact that we live in a country full of temporarily embarrassed millionaires, it is still a low %age chance of actually happening

Apparently, 25% of Americans over age 50 are millionaires by wealth, and so if you don’t expect those figures to go down, your odds of living to be a millionaire are pretty good!

https://www.fool.com/retirement/2024/05/27/heres-how-many-mi...

Yeah yeah, illiquid household wealth … but millionaires nonetheless.