It used to mean something more than it does now. I noticed ex-Googlers were well above average in 2012, now they can be below avg. I have a colleague of mine at my current job that makes a point of being an ex-Googler but they only worked there for 6 months, so it is kind of meaningless.
It's always been a distribution. Some are amazing, some are normal, others are less than normal. They're all really good at the handful of things Google screens for, but otherwise it's just like any other distribution of developers.
As a hiring manager I view Google on someone's resume as a non-signal. If however they are the sort of person who draws attention to having worked at Google I view that as a negative signal.
Global average or people-who-work-at-FAANG average?
The frame of reference here is important, otherwise average is pretty meaningless since we have no objective list of what an average developer consists of.
