Whether you agree or disagree with the guidance here, you have to respect the effort that has gone in to put this together. Especially good in understanding the role of the corporate recruiter - not a friend, not an enemy - though I would add nuance such that they are not a friend but become a friend once you secure the endorsement of A N other assessor.
1) Recruiters often have quotas too - In many cases, their own performance is measured by hitting hiring targets, so they're incentivized to get you in the door, even if not on best terms for you.
2) In the age of initial RSU stock grants, underleveling can be VERY, VERY costly. The difference between L and L - 1 could be > $100k/year, so the penalty may be far more severe than just time, especially if annual stock refresh is based on level as well.
3) Coding interviews aren't supposed to test knowledge of specific algorithms, but I've been part of a hiring committee at a FAANG and had to request another round of interviewing a few times because the original interviewer failed the candidate based on a chosen coding question that had to do more with knowledge of matrix math, graph theory, etc. than the ability to take a problem, break it down, consider edge cases, and produce code.
4) The process is indeed very arbitrary. My favorite story is about a time I submitted my resume and got a call from a recruiter two weeks later who loved my background. I interviewed and got an offer that I eventually declined. I learned during the process that my application was rejected by the company's resume scanning software. It was purely a coincidence that a recruiter happened upon my LinkedIn profile (which mirrored my resume) at nearly the same time.
I had something similar happen to me. I submitted my resume on the company's career page after seeing a role that matched me perfectly. I got an automated email telling me I wasn't the right fit. Dejected, I posted my resume on a job portal only to have a recruiter reach out to me for the exact same position. I interviewed and got an offer.