Broadly, I think the answer is yes. Yes they do.
Broadly, I think the answer is yes. Yes they do.
Sure, some founders have gotten filthy stinkin' rich off their startups, but those are lottery-ticket odds. Most founders seem to be aiming for either a self-sustaining small business or an acqui-hire, both of which are middle- to upper-middle-class career paths, but neither are by and large own-your-own-helicopter-class career paths.
That said, I think the answer hold even if you restrict the question to small self-sustaining lifestyle-businesses-size. You correctly state that there is no way of knowing how big a company will get at founding time. However, if there's an upper limit, then this may significantly affect risk evaluation. People will respond to the incentives they see, and you can't kill the incentives without affecting how people behave.
In a broad sense some people don't respond at all to incentives (assuming monetary) and others do respond but its not a recipe for personal happiness.
Personally, that's why I'm such a fan of some sort of basic income. While it reduces inequality it keeps the monetary incentive response as a choice, which ultimately equals more personal freedom.
No basic income is going to make people feel useful and productive. Personal freedom isn't the same as personal fulfillment, after all. Basic income also isn't going to change the kind of inequality you see in the Bay area - where highly skilled professionals make multiple times the basic wage.
I assume you mean some kind of basic income indexed to the local cost of living. Without that people would need to do what people will raise nine kinds of Hell to avoid even thinking about - moving to an area they can afford.
Anyway. I don't think it's an easily evaluated question, in large part because there are good ways to fight poverty (as a government) and ones that are no better than cash-fuelled bonfires. It's difficult to evaluate a kinda-sorta-semi-vaguely-known (change in private spending from higher taxes) against a total unknown (result of hypothetical anti-poverty programs), though.
Which is a long-winded way of saying you're right about it being a quantitative question, but I don't think it's a readily answerable one.