That doesn't really make a difference. Opt-out is essentially the same as just forcing it. The vast majority of users will never even know that they could be opting out.
IIRC, you're properly asked, the first time you try to do something, whenever you want to enable relevant tracking - e.g. share location history (e.g. when trying to set up "show my location"), or save voice data on Google servers (e.g. when setting up voice unlocking), etc etc.
I'm not exactly sure about app history and in-app search, though - just honestly don't remember about it. But it could be that user is actually asked at account setup time.
Point is, for many things Google actually properly asks for permission. Guess, it works for them, because timing's relevant. (They probably have ton of invisible tracking as well.)
Is that true? You can turn off your ability to see your activity history in Google, but does it actually delete (or not send?) any data from Google's servers?