microG still sends data to Google though, I believe, even though the local code is open. Without Google involved at all, Android is barely usable as a daily driver. I tried for a while.
It keeps connection to Google, but at least does not send your location and does not help Google with personalizing ads. I'm also not logged into Google account.
When all I needed of my phone was web browser + YouTube playlists + FB Messenger, lack of Play Services did not seem to be big deal.
Basically it still uses Google backends and infrastructure for push notification delivery without contributing anything to the costs of the infrastructure. It does that by spoofing the library ids and accessing the APIs with fake authorization.
I don't think that's a sustainable plan going forward.
