A Google login, whether you get it via gmail or "G Suite", ties into all of the Android apps and keeps search history and integrates it into other Google products, and runs synchronization of most app data so they can see a great deal of what you do on the phone. About the worst that you can do is turn on device management. It will take about two days to turn off and during that time it will do its very best to force your email users to put their devices under your control. After that you apparently even have control over booting of the device.
It's enough to make me want to support another open phone. Mozilla just gave up the ghost on that.