[0] https://en.wikipedia.org/wiki/The_World%27s_Billionaires#Ann...
Bezos' stratospheric economic "mobility" is not evidence of a more generalized economic mobility. In a system that is even vaguely capitalist, there will always be people who become incredibly wealthy without inheriting most of it. Their existence is not evidence of "considerable mobility", it's merely evidence of some sort of capitalistic economy.
The fact that the 10 richest people on earth were not born into stratospheric wealthy is a testament (of sorts) to capitalism; if you want to know about economic mobility, you're better off focusing on statistics, not the exceptions that prove the rules.
Is that the social mobility that we care about? Anyone who is willing to work hard and already has the means to attend an Ivy League school can become a billionaire.
Jeff Bezos, Larry Ellison, and Sergey Brin were NOT top 5% in the USA. Depending what period in his childhood that you look at, Sergey Brin wasn't top 5% in the world either. (His family was educated, but they arrived in the USA as refugees from the Soviet Union.)
Several others started with rather less than you might expect. For example Elon Musk arrived in North America with only a few thousand dollars to his name, and had to work manual labor to get by. (Yes, his father was a businessman, but the two of them have a..difficult..relationship.)
It might just be that you are the lucky one, and by definition, are surrounded by other lucky ones who landed similar jobs. Many millions others might have tried and failed and live in poverty or are dead. You'd need data on all those millions to talk about the % chance of someone succeeding, and to show it's better here vs there.
But that's all unhelpful. I think hope is important. I'd love to see us have a national consensus around equal opportunity, egalitarianism, and tolerance to different ways of life (and not just the "different" that I agree with!).
Ah, the good ol' days.