Assuming the public interest ("PI") people all meet the GPA cut-offs at biglaw, then the fact that these feeder schools (e.g., CCNP) can still manage to send 60% of the class into biglaw is even more impressive and indicative. Say 10% of the class at Columbia get PI jobs while meeting biglaw GPA cut-offs, and Columbia still manage to send 66% into biglaw, that means you only need to be in top 76% at Columbia to get into biglaw instead of top 66%.
On the other hand if the PI people do not meet the GPA cut-offs and can't snap a biglaw offer even if they want to then they are not tipping the scale at all. Those grads who are able to get federal clerkships are def in the top of the class let alone above biglaw cut-offs.
You may say the situation is different at HYS, but not everyone can get in HYS. Quite honestly if OP can get into HYS then this post is prob moot considering HYS give pretty substantial PI grant and biglaw might not be the ideal outcome should OP favor other career options. "They literally cut me a check for 11K every 6 months for loan payments."
Higher placement in big firms also shows that firms in turn are willing to hire more from these "target schools" and be more flexible in terms of GPA. School alumni relationships does matter. e.g., Kirkland hires more from Northwestern and Gibson Dunn prob hires more from NYU (location also plays a big role here). These relationships may not mean much if you are acing 1L classes but I'm pretty sure Northwestern/Cornell is gonna serve you better than Berkeley when you are in the bottom half and paying for sticker price.