ideally things go perfectly all the time, but people sometimes make mistakes. what would you rather they do? pass on the candidate because they didn’t get enough data to support a hire? or give them more chances to demonstrate their capabilities?
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.