How many Harvard Law grads do you know? Or Columbia or NYU or Berkeley?
I mean, you can't get into Yale unless you have great grades in college, excellent LSAT scores, and if you don't have other accomplishments (e.g. Rhodes Scholar, etc), it's a crapshoot to get in. I did not get accepted to Yale, even with my LSAT. That was fine because it functioned weirdly as a safety school of sorts. I wanted to go to school in Boston, New York, Philly or DC (this was before I realized I hated DC). If I didn't get into the top 10 law schools in those places, I didn't really want to go to law school -- but I thought I'd make an exception for the #1 rated law school. Not that it was likely I'd be accepted there and not elsewhere (the reality was completely opposite; I got in everywhere but Yale), but they waved the application fee so why the hell not?
So obviously there is a certain threshold of academic excellence to get in (unless the standards are lowered, as they likely were for Vance). And a lot of excellence comes out. But every school has duds and weirdos. Yale produces more of the latter than the former, but on occasion there are grads who are both. I think the difference in intelligence, law ability, or any other metric you care to use between the average Yale student and the average Harvard, Columbia, NYU, Stanford student (etc) is close to zero.
Well, that's my experience at least. I worked at WLRK and then the appellate practice at Jones Day and then taught law, so for decades most of my colleagues came from those schools (and also I attended a Top 5 law school), so I have a pretty rich experience.
One thing that always bugged me about Yale grads was their tendency to conflate the sentences "not all X are Y" and "all X are not Y." Yes, that logical error shows up countless times in law review articles, judicial opinions and the like. I find it hard to believe that Yale is teaching that. My guess is that a) the prevalence is about the same, but I first saw that from a Yalie and then primacy bias took over or b) I've been exposed to a sample that skews that way. If there are an infinite number of traits, even a purely random sample will exhibit some of those traits disproportionately. But anyway, in my experience, Yale Law grads are particularly susceptible to that illogic and I really don't understand how or why.