Google has quarterly "calibration scores" that are assigned by management, but require a lot of political in-fighting because there's a forced curve across the company. You don't see your score but only get a range. "Meets expectations" is what most people get and it's a huge range: from 3.0 (can't transfer, borderline for a PIP) to 3.4 (above average). What this means is that you're managers can smear you and you have no idea that it's happening. Evil much?

Then there's a semi-annual Perfolympics in March and September, which is peer-review driven (engineers drop everything for about 2 weeks to write reviews) but has all sorts of boondoggles that are easy to abuse. For example, there's unsolicited feedback and even manager-only feedback that you don't see. Google routinely has to pay out settlements because of aftermath of this system. If you work in technology, chances are that you know a couple people who've collected six-figure settlements because of things said about them in the Perf system. Needless to say, this only gives Google further incentive toward secrecy.

Also, Perv really is a "permanent record". A bad Perf will block you from getting promotions and transfers 5 years later.

Google is nothing if not abusive with data, although in this case, I'm hesitant to call that deeply subjective garbage "data".

You are spouting nonsense sprinkled with vague half-truths. You have a distorted view of what one part of Google might have been like for the short time you were there.

There is no forced curve. One of your "Perfolympics" is actually optional. Perf is technically a permanent record, but promotion committees will rarely look back beyond one or two cycles (e.g. up to a year). Five years is nonsense.