NYT article on Supreme Court clerks, but it also includes a study of the makeup of HLS classes.
https://www.nytimes.com/2023/02/06/us/supreme-court-ivy-league-harvard-yale.html
Relevant excerpt (emphasis mine):
"The study, which considered 22,475 Harvard Law graduates, took account of three data points: where they went to college, whether they qualified for academic honors in law school (graduating cum laude, magna cum laude or summa cum laude) and whether they obtained a Supreme Court clerkship.
About half of the graduates had attended one of 22 selective undergraduate institutions, and more than a fifth of the graduates had gone to college at Harvard, Yale or Princeton. Both of those groups graduated with honors from Harvard Law at above-average rates.
But here is the key point: Even controlling for achievement in law school as measured by academic honors, members of the two groups were more likely than their peers to obtain Supreme Court clerkships. And most of the difference could be traced to students who had gone to college at Harvard, Yale or Princeton."
While there is certainly a high degree of correlation (top 22, HYP undergrads generally being high achievers and good test takers), the extreme over indexing of undergrads from those schools suggests that is also an element of causation.
As for the OP, if Penn is not affordable, it is just not an option. A free education at Oberlin sounds pretty good, and I don’t think there is any huge advantage that Penn has over Oberlin.