I left Google for a startup and got basically half the total compensation. 6 years after leaving, I am making about what I did at Google 5 years ago and 2 "levels" lower. If I stayed at Google, I'd be making about $800,000 a year.
You should really really ignore the distasteful feeling about being grilled by a bunch of strangers and just do it. (I actually really enjoyed my Google interviews. Problems I hadn't seen before that I came up with interesting solutions to.)
For anybody that needs reminding:
Companies' abrasive or uncoordinated interview processes likely has nothing to do with your experience in your team on the company.
Your manager's uncollaborative behavior may have nothing to do with your day to day, or mental health on the job.
Ignoring or leaving any of these companies because you considered any one behavior a red flag is a privileged take for people that have trust funds, masquarading their version of life as normal.
Take a contract position or something else less hard to get, get more financially secure and then go for the faang role.
As to "not enough data"... how exactly? If there is a list of things to check off that is to be distributed amongst the interviewing team, there should never be an issue. If people are winging it and just happen to ask repetitive questions then everyone asked what they needed to know and signal should be there.
It sounds like Google's process is fundamentally buggy. They should fix that.
Unfortunately, it's really hard to quantify exactly what's broken about the interview process in a way that justifies (to the appropriate individuals!) upending the status quo. You and I can both complain about how this is terrible for candidate experience and for hiring the best talent, but that's not going to change anything.