That doesn't sound like an effective pipeline to me. That sounds like a really bad pipeline, and a lot of post-hoc justifications to minimise the issues.
I'm hesitant to take Google's use of a tool as an indication that the tool is good, or that the process is refined. They used brain teasers for years before figuring out they had zero predictive power. Ignoring the implications of the scale of that mistake, one thing it indicates is that they aren't able to effectively evaluate different interviewing methods.
If they had no ability to effectively evaluate, how did they conclude that brain teasers had no predictive power?
I see google's process along the same lines as "democracy is the worst form of government except all those other forms that have been tried".
Now ideally, what you'd want is to be able to perfectly read someone's mind and someone's intention, to be able to tell instantly their strengths and weaknesses, to be able to tell which of those weaknesses are trivial ones that will get smoothed over a week into the job, and which of those are ones that are actually long-term issues that will poison your organization. It's possible that individuals with such judgement exist (Paul Graham has said that YC's success was attributed to Jessica's ability to judge founders) and that they work at google. But now you also need a process that can interview and evaluate a thousand people every single week. So what works for small companies where you can agonize over every hire or for exec searches, doesn't make as much sense for mass hiring of peons.
So given those constraints, everyone knows your process, everyone wants to apply, you need to interview a thousand people a week and decide to hire a hundred of them, and they really don't all need to be rockstar founder quality, but they all need to be able to produce something, you can start to imagine what type of interview process you might end up with.
I'm hesitant to take Google's use of a tool as an indication that the tool is good, or that the process is refined. They used brain teasers for years before figuring out they had zero predictive power. Ignoring the implications of the scale of that mistake, one thing it indicates is that they aren't able to effectively evaluate different interviewing methods.