Learning is hardly a thing at startups. So many people are incredibly junior and know nothing about the industry or tech to begin with. (I mean, who else would take such low pay?) Yes, you can get to get pushed into unqualified roles and learn from it - depending on who you are. But that's really only at the cost of others - you're maximizing for one person and not the group. So it's really a startup is a system that maximizes the happiness of only a few individuals - which we already know with how stock gets treated. (Founders frequently being the only ones who get rich no matter how early on an employee you are) e.g. Wow, X got promoted to be the team lead/manager. X is definitely not qualified and, in fact, makes the most productive members of the team more unhappy by being a manager now. This only happened because the rest of management is desperate, broke, and can't afford anyone who is a good manager. People under X will leave the company. I've seen it happen a lot at startups and it results in crazy churn. Same with more technical decisions. Seeing people promoted to Senior/Staff who have are barely better than their junior counterparts (just more arrogance). A lot of folks recognize dumpster fires when they see it and bounce. They're is also so little growth opportunity once those positions are taken unless you're on a rocket ship.
In terms of learning tech: A lot of tech is also outdated at startups compared to big N. There are large enterprise companies that are using even older tech but there's no reason to join those as they pay on the same scale as startups (And your job security is no better than at a startup). Scaling problems only exist once you've hit rocket ship status (so who cares about anything) - whereas they're everywhere at a big company. There are startups that are trying to use the latest and greatest and do interesting things but the number I interview with who are using outdated tech seems worse than any Big N I've interviewed with. Big N seems to be way more cutting edge (because they can afford it in terms of resources and know it attracts talent). Upgrading tech at a startup only happens when the company finds out no one at $Y salary with Z options will join the company until the company updates their stack. It's not like they can really afford it anyway. The company is so focused on churning out features and pivoting wildly to extract any bit of $$$ that they can out of the market while they find their cash cow (cash cow being actual profit $$$ or just magic numbers that can increase their next round of funding).
Anyway, back to my point about selling a startup short, I think the only reason I'd truly consider startups is being able to choose the people you work with and the problems you solve (although that could change easily once the company finds out it needs to pivot - again). There was nothing about that here and it's obvious from reading the article that it's all about that but it's not brought up. You chose to work with your brother and all these folks. You don't get these choices at a big company. You're mostly thrown together and just deal with it.