Ask yourself this, would your "startup within a big company" have managed to lure Mark Zuckerberg or Larry Page to join them instead of founding their own compa

Ask yourself this, would your "startup within a big company" have managed to lure Mark Zuckerberg or Larry Page to join them instead of founding their own companies? And even more important, would it even let such people have lead a significant part of the company in order to realize their ideas? If you answer no to either of those, there is your answer to why your "startup within a company" can't hit it as big as real startups.