Sure, you can distort what it means to protect your privacy and security to a point where feeding all your info to Google is still within that realm, but I don't think many people would agree. I'm not entirely sure what the sandbox does for us, since every app that uses Google Play Services can communicate to each other regardless. My understanding is that the sandbox just keeps Play from being able to see eeeevverrrything else that's not using the service. If I'm wrong, I'll happily eat crow. Oh and I'd love to see that post from Mastodon, if you have it.
Look, I'm in the same boat, I just got this new watch, but I know damn well that my privacy is completely destroyed by having this, and the associated services/permissions enabled. I'm slowly chipping away at actually de-googling (which is the main threat to our privacy on Android,) though until then I won't fool myself by thinking I'm somehow incognito.
I think a lot of people, (myself included,) would probably go 100% de-google immediately if we had some sort of app that would give us a clear dashboard of everything our phone/watch is sharing, in real-time. Enable a service, change a permission, and see in plain text what info is being shot over.
I'd also love more-granular control over these services, and I'd be interested in revisiting the spoofed play services stuff from MicroG.