- after stopped using Google Play services/framework and replaced it with microg, battery life improved for 30% with same programs beeing run and same settings without losing any functionality, this is the most obvious part that something is going on and it is hard to deny. I never used (while on google play) any syncing, gps fix and so on. Meaning exactly same settings, same programs, no google applicatios (maps,...) same AOSP rom, not even factory resetted in between, just no Google Play presence on same phone. I switched to microg as I have figured out that whatever I do can't stop the Google Play services/framework communicating with google (firewall, xprivacy,...)
- there are hidden sync in Google Play that can't be disabled and are syncing regardless of your settings (https://www.reddit.com/r/Nexus5/comments/270axz/enabled_reve...), like Location reporting (not the one visible, there is second one, you will need root to see it, you can disable it but it will automatically turn back on after a while).
- DNS is defaulting to google dns 8.8.8.8, it is overriden in most cases by router settings but still.
It is up to each person to decide what this means but I would seriously suggest looking at https://lineage.microg.org/