TripleBytes' placement rate was 40% in 2018 [https://techcrunch.com/2018/02/28/triplebyte-has-raised-more...]

I'm not sure how to reconcile a recruiting company well-known for doing rigorous technical screening having a 40% placement rate, most candidates being a clear yes or a clear no, the hiring process being completely fine, and the hiring process not producing many false negatives.

A 40% placement rate implies triplebyte has the hiring bar lower than companies want it to be. Ie, even with rigorous screening, they have a high false positive rate. (Well, that assumes candidates are totally ordered by desirability, which is not at all the case).