There's a good essay in the psychological/social condition (rather than just the direct economic position) of smart upper middle class young adults, and why Altman observed founders disproportionately coming from that background

Obviously by definition there are very few "super successful" people so it could still be that their offspring have an even bigger advantage than the UMC kids and it's obscured by their scarcity, plus thanks to homophily Altman is gonna know more UMC people anyway but

It does seem like UMC kids have some unusual advantages in building new things even beyond what you'd expect given their economic status (can afford to risk a career year on a new biz, likely to have savings, not supporting parents financially, good education to fall back on etc)

Founding anything is often the product of years of abstract thinking with no immediate payoff which most people cannot afford to do, and in many social worlds is seen as a wasteful indulgence

UMC kids are secure enough and even encouraged to spend some slack thinking about 'useless' things in the short run until they notice a market gap in the longer term (obvs this is downstream of economic position but it's not as direct as 'rich parents invest in your business')

They get exposed to a lot more information by osmosis, see other countries more, and get to think at a larger geographical scale early on. The pandemic illustrated just how rare it is for even senior people to notice what happens in other countries- more UMC kids get this early

IME the least-noticed UMC asset is their status budget: a lot of people feel huge external social pressure from family, media, etc to work somewhere people have heard of, they need to worry about not looking poor, and they don't have a network outside their job

UMC kids start with a bigger network (encouraged early on to meet new people) which isn't dependent on their job/income, and have social status (and more contacts) via their education and experience, so the social costs of trying a new thing are much reduced

Founding new things is weird, a challenge to the existing order, people will be hostile to you or look down on you. Much easier to deal with from the UMC starting position, which is an additional reason that UMC people seem to disproportionately do new or strange things

Tldr: UMC kids are more likely