You are perfectly describing Google's strategy with maps. Lump together traffic updates and "rate this place" (even though I didn't rate the last 100 times), to create as much all around disgust for your brand as possible.
Notification categories is not exclusive to google apps, of course (OS level feature as long as your app targets Oreo), but their apps tend to give you very good control over what it shows you.
So, I'd disagree strongly that this is a google "strategy". It's more a problem that their apps tend to have a lot of features crammed in.
Of course, I don't know how this works on iOS (I'd be surprised if it's not in the settings somewhere? It's in their interest that you don't disable all app notifications)
It doesn't matter much to me if the problematic behavior arises from strategy or accident, though.
Adding the ability to turn this stuff off is good, but it should be default.
Edit: They definitely have, since I have those options now.