> the estimated 40-80% contribution that genes make to people's intelligence, conscientiousness, and work ethic is much more likely to be at play, here.
I don't think you really need to get into genetics to explain anything here. Some people get lucky, their children inherit their wealth and maybe squander it after a few generations, or maybe they don't. Neither the parents nor the children need to be particularly smart; they just need to get lucky.
Using money as a measure of intelligence is very risky. On the one hand, sure, everyone wants to be filthy rich (presumably) so there's a lot of competition. On the other hand, there are large swaths of the whole world population that will find it impossible to be the next Zuckerberg or the next Bill Gates- say, a daughter of a Bangladeshi weaver is probably not going to travel to Silicon Valley and fund the next unicorn startup, sell it for billions and bequeath some of them to her children.
That's not because of a difference in intelligence with someone who will follow that path. It's because we can't fit 7 billion people in Silicon Valley, and a few tens of thousands of jobs in tech.
I guess you can argue that the people who are already in Silicon Valley have some sort of genetic advantage but unfortunately that way lies a whole bunch of very gnarly racial bias that is going to be extremely fiddly to untangle. Therefore, see above: using money as a measure of intelligence is very risky.