It's nice to see they have an easy to get to Delete My Activity feature but I have to guess that it deletes it only from the perpective of me being able to ever view it again.
I wouldn't be so sure (though I have not looked into it)
Google already has to comply with European right to be forgotten laws, and my recollection from formerly working there was there was a pretty advanced system to make it very easy to store user data tied by an ID coming from the many diverse apps within Google, in such a way that it could all be deleted upon request in an effective way that even accounts for backups, by having all data being always encrypted at rest and in transit, so then only the encryption key would have to be deleted.
So from a technical perspective, it'd almost be easier to make it really delete it, than to not, since you'd have to not use the obvious default internal platform for user data storage.
At least, that's my vague recollection. I never coded against that particular API anyway. Cool idea though.
Don't confuse Google with Facebook and Uber. The different software giants have very different cultures. Google doesn't mind moving fast but not breaking things is very core to the culture, much more so than is at all common in software or IT.
https://news.ycombinator.com/item?id=16685179