3 Larry Ellison, born to an unwed mother, adopted by family members
Adopted by family members yes. Wealthy ones.
10 Michael Bloomberg, gather was a real estate agent, grandparents were Russian Jewish immigrants (not a group known for being wealthy)
His parents were middle class at least during his formative years, certainly not poor. It's a little unclear what his father did, some sources say bookkeeper and some say real estate. Varied business interests? In any case
11 Jeff Bezos, while his mother came from a ranching family, his adoptive father was a Cuban immigrant
So, his mother's family were rich and she married someone who might not have been rich. I'm not sure how that makes him not from a wealthy background.
12 Sheldon Adelson, father drove a taxi cab
Mother ran a knitting shop. Not that it made them rich, just wondering why you only count the fathers.
13 Sergey Brin, born in the USSR, came to USA with parents at age 6
Father a math professor and mother a researcher for NASA. Once again, not rich, but definitely middle class.
15 George Soros, while his parents were not poor, they were Jews in Hungary when the Nazis invaded
Mother from a reasonably well to do family and lawyer father. Not necessarily rich, but far from poor. So middle class background and family connections.
How many more do I have to list before they are no longer the outliers?
Well, it's a list of 400 (and the whole list are outliers just from being the richest of the rich in the first place), so I would say you have to list quite a few more.
In any case, I don't have a lot invested in this argument. Arguing about the mega-rich doesn't really say anything about the poverty trap, even if every person on the list actually came from abject poverty. For some reason, some people always want to focus on the mega-rich. It reminds me of arguments about, for example, mixed-gender youth sports teams, where there's a certain type of personality which will always focus on professional sports teams. It doesn't make any sense, as they are statistical anomalies anyway.
The thing that gets me is that you're still apparently convinced that Sam Walton's heirs and their heirs are somehow proof that people on the Forbes 400 list aren't descendants of wealthy people. I have to admit that you have solidly disproved the absolute statement made that "all of them come from at least upper middle class".