Privacy on a non-degoogled Android device is non existent. Just because only Google gets to munch on your data doesn’t equal privacy.
I suspect the issue people have is that it is not possible for the average user to confirm that a block like that is working 100%. Seen as google control the OS they can just route their traffic around a block like that if they wish. Sending the data over 4g would mean you don’t even see it on your network traffic logs. There are a number of reviews suggesting it intermittently lets aupposedly blocked traffic through too, but the biggest issue maybe the way it works. As far as I can see, it acts as a VPN, but that means it won’t work well with other VPNs, which is another way the traffic can leak. Basically, installing an app like that doesn’t degoogle your phone at all, it just makes you feel like you’ve stopped your data leaking.