The definition of "success" is different between a bootstrapping business & a VC funded business. A consultant can define success as "making enough money to live off of". A VC funded business has a different definition.
So how would a study be conducted? A survey asking if the business was "successful"?
Actually, that's not a bad idea. Surveying founders at 5, 10, and 15 years after founding whether they were happy with the outcome could be enlightening. A little bit like the 7-up documentary series. It would be very interesting to see which path tends to provide the best outcomes according to the founders.
So how would a study be conducted? A survey asking if the business was "successful"?