I also did interviewing at a FAANG and this was not my experience.
1. We trained 4-5 times on each type of question. The first few were shadows, and then we did reverse shadows where someone watched us give the interview and gave feedback later. In one category I asked for and was allowed to reverse shadow an extra 1-2 interviews.
2. There was auditing. In debriefs where you discussed the candidate and reviewed notes, the debrief lead was supposed to closely examine what questions you asked and how you conducted the interview, with the explicit goal of making sure that the interview was conducted within spec and your recommendation made sense given performance. Shortly after I was certified to do interviews, a debrief leader (correctly) identified a major issue in an interview that I had conducted. That candidate was given another interview in the same category. Although I didn't face any official sanctions, it was definitely an embarrassing experience and made me handle future interviews more thoughtfully.
Overall, I was fairly comfortable with the rigor of the process that I saw. I'm certainly not saying the process is perfect but my experience did not align with yours.
Not if it's taken too far, as it will create new biases based around the "rigor" of the process. You end up "hiring to the process" as opposed to "hiring to the team / role". If someone doesn't have enough experience/knowledge, but they are clearly talented enough to learn on the job and look like they could accomplish great things, that person may be a much better fit than someone who knows everything but is terrible at executing or working within the structure of a large organization.
(the "lizard brain" is a myth by the way; I think you're confusing it with unconscious bias of heuristics, which is not what the triune brain theory was about)
1. We trained 4-5 times on each type of question. The first few were shadows, and then we did reverse shadows where someone watched us give the interview and gave feedback later. In one category I asked for and was allowed to reverse shadow an extra 1-2 interviews.
2. There was auditing. In debriefs where you discussed the candidate and reviewed notes, the debrief lead was supposed to closely examine what questions you asked and how you conducted the interview, with the explicit goal of making sure that the interview was conducted within spec and your recommendation made sense given performance. Shortly after I was certified to do interviews, a debrief leader (correctly) identified a major issue in an interview that I had conducted. That candidate was given another interview in the same category. Although I didn't face any official sanctions, it was definitely an embarrassing experience and made me handle future interviews more thoughtfully.
Overall, I was fairly comfortable with the rigor of the process that I saw. I'm certainly not saying the process is perfect but my experience did not align with yours.