You are going to get in the trenches with the next generation of self-selected future business leaders. These are the people that will form of the nucleus of your professional network for the next 30 years.
YC is like a new elite graduate school / bootcamp for startup entrepreneurs. Just like not everyone gets into HBS or Saïd or INSEAD, not everyone gets into YC.
B-school is getting more startup and entrepreneurship oriented, but is still aimed, for the most part, at general management at mid-sized and large mainstream firms.
They're too small and there's not enough of them to fulfil that role. Additionally there aren't very many non-tech areas with yc-type programs for them.
That doesn't mean it has to be that way, does it? I wasn't implying that the yc model is a replacement today, just that it perhaps could be in the future for at least some subset of people that are currently going to business school.
You are going to get in the trenches with the next generation of self-selected future business leaders. These are the people that will form of the nucleus of your professional network for the next 30 years.