> One thing recruiters can still good for is post-interview feedback. Some companies feel more comfortable giving it to recruiters than directly to you.

Echoing this. In fact, it holds true even for in-house company recruiters, as long as they feel you are a reasonable person and are comfortable disclosing it to you (without fearing that you will start causing problems due to finding out this info). Yes, even FAANG-level recruiters can be ok with that, but that's on a case by case basis.

I personally noticed that over the years (as I got better at interviewing and at communication in general), recruiters themselves would start going "technically I shouldn't be telling you this, but..." more and more frequently. And no, I never asked for "more detailed feedback", they just decided to volunteer it themselves. I can imagine that asking it directly would have been fairly awkward, ("but can you give me the real feedback instead of what you just gave me?")

And the wild thing is that they weren't bsing or just giving me generic "sorry it didn't work out, practice your algos and systems design more". They would give a pretty detailed feedback, half of which would match the stuff I already knew about my performance on those interviews (e.g., "I felt I did poorly on interview #3 due to me not being able to efficiently optimize this one approach and then maybe being a bit too vague during systems design round in the beginning"), which acted as my personal litmus test on the legitimacy of the feedback. And with the other half being brand new information that actually opened my eyes to some blindspots I've been totally missing.

It's to the point where you can usually copy paste a few lines of job description from the recruiter's email with the "brand new opening at a confidential client" into Google and find the original posting from the company.