I'm not sure I believe any of this. Very little of the work we do at Google involves feeding data to some tool and sitting back and watching the results. It's software engineering and problem solving as usual, just with some nice libraries and tools to save time for the hard parts.
I'm especially confounded as to what SRE tools would cause someone to "not meet the hiring bar" by responding to a question by saying "I'd just use some proprietary technology". I can't think of any tools that are useful enough to be the singular answer to an open-ended question, and I can't imagine anyone wanting a job saying "just use this tool you've never seen before" in an interview. It's unbelieveable.
Being used to certain tools is not specific to Google, either. If you ask a Python programmer trivia questions about Ruby, he's not going to know the answer. But given a week, he'll probably know the answer.
Another Googler I talked to said that their stack is unimaginably huge, and nobody knows how all of it works, which was (quoting) "probably by design." Make of that what you will.
The stack is big but there is nothing preventing one from understanding other than that it mostly works and so one is not forced to understand it. The code is there and you can start it all up locally on your machine, so I don't really see the problem. It's not huge to keep unhappy Googlers from finding other employment opportunities, as you imply.
Anyway, I can't believe I replied to this post and am now going to click the reply button, but here goes...