I found this super vague. In what way will people be more productive at a startup than they would be at an established company? And why does that mean that startups are a good thing?
One way you could make this clearer is replacing the phrase "can be much more productive" with a more specific goal that's more obviously good. Will startup founders learn and grow more in a shorter period of time? Will they have a larger positive impact on the world than they will at an established company? And if so, why?