Neither my brother nor most of his friends at Vanderbilt were burdened by student loans. Most came from reasonable wealthy families that were able to pay the cost up front. Reasonably well-off families send their kids to Vanderbilt and other top schools because of the connections that can form and the reputation of the school. Everything else you mentioned comes second.
I'm not sure what point you're trying to make here tbh. Nobody is arguing that wealthy and connected individuals in part maintain those wealth and connections by going to elite schools. Legacy admissions all but guarantee that once you're a couple generations deep you'll be able to at least maintain your family's status.
The question is whether a college charging $400K for what is probably closer to $70-80K of services is right.
The point is that the parents who are paying for their kids to go to these schools have already put aside the money in a 529 or other account, and if their kids get admitted, there is no question of cost to put their kids a step ahead. Given this, exclusive universities know that they can charge prices that are relatively extreme, as they don't have any financial, moral or legal obligation to not do so. The question of cost compared to earnings that you raised is immaterial for these students, as the students will bear none of the cost.
