I wonder if there is a good way to measure documentation quality...I suspect such measures will require techniques borrowed from user experience research.
I would start with a checklist:
- is it complete and consistent
- is there a description to every important piece
- working examples
... and if this is complete, you can measure all you want, but I would start with the basics.
For Google Cloud Platform, they partner with other companies (like the one I work for) to help with GCP setup. This partner program was started in the last few years, so I don't think they were doing this for Android back when Android development was new.
Also, the company I work for spent a lot of time building Android apps for Fortune 500 companies, so I feel like I would have heard about it. Our clients would have benefitted from having Googlers build Android apps and train people!
Because of all the junk they've added re: battery optimization, "Adaptive AI" notifications. Even after disabling much of that, it takes a 3rd party app to get notifications reliably.
My coworker and me are already starting to feel the pain on various core APIs, the latest being notifications, which according to my coworker had 3 full revision, and finding documentation for the last one is hard. Storage (with Android 11 modifications) is another place where the documentation is starting to get stale. Those are not the only APIs were the documentation was poor.
In my opinion, Android documentation is at the same place iOS documentation was about 5 years ago (before they started removing entire pages from the documentation) : overall very good, but a few places were it's not up-to-par or downright horrible. I don't expect the quality to improve in the future.