You seem to be now arguing that prestigious universities provide a WORSE education than lower-tier institution. That's very different from what you said in your original comment, which is that they're no better. The latter is probably true, or at the very least not dramatically better. They certainly don't offer a worse education, though.
So the additional competency from direct instruction is negligible. That doesn't mean that the value of attending a top-tier university is negligible, because the direct instructional education is only a small part of what someone gains access to at a university.
There's the social network aspect: There is a lot of value in having personal connections with other successful people. People need business partners, investors, advisors, etc. in order to be successful, and top tier universities intermingle you with others who are likely to be helpful in those regards. At top tier universities, the majority of people you interact with will either talented, wealthy, or both. At a lower tier university, the pool is far more diluted, reducing the utility of your social network in pursuing success.
There's the branding advantage: if you're choosing between two people, and one has someone you trust vouching for them that they're competent, and the other doesn't, you're going to go with the first person every single time. A top-tier university is basically that third party, vouching for its graduates: they're more likely to be successful, and people want to surround themselves with successful people.
And then there's the educational advantage: If you're surrounded by other smart, motivated people, you're going to gain real educational advantages by cooperating with them. You learn from each other, bounce ideas off each other, etc. If you're by far the smartest person in the room, you don't get nearly the same added value out of your education. At a top-tier university, you're going to be surrounded by substantially more high-quality students than at a lower-tier school.
And yeah, convincing people to give you money is BY DEFINITION valuable. As measured by the value of the money they're giving you.