For your example, you need to do a post-graduate degree (law) from the Ivy+. This article is talking about the gating functions of the undergraduate admissions departments.

The graduate school admissions officers are far more likely to consider strong candidates from "normal" universities than their undergraduate admissions colleagues are to consider strong candidates from "normal" public high schools.

Also, consider Harvard Extension. People shit on it constantly and call it the backdoor, not-so-honest way to get associated with Harvard. But in reality, it is more of a front door into a "make of it what you will" program. A significant number of the people that actually graduate use it to get into high-quality PhD programs that would have otherwise completely ignored them based on their past and their lack of "proper" pedigree.

In my mind, the undergraduate portions of these universities are pretty much lost causes. But their graduate schools are far more meritocratic and, much more importantly, fixable without burning everything to the ground. Because if you want to burn it all down and start over you are going to have to fight against all the rich and powerful people, and probably aren't going to win.

I don't know if it's intentional but you're conflating mutually exclusive lines of thought.

The argument that such decisions should be made at age 22 instead of age 18 doesn't support — in fact contradicts — your argument that trajectories toward SCOTUS should not be related to law school admissions (which do indeed happen at age 22 instead of age 18).