Sometimes when owners shared things like idle battery drain, it's really unclear about the duration they left it, just simply said overnight.

Things like this really hard to draw a clear line. I also can say I had 0-1% drop overnight on my S6e.

Well, firstly I never install facebook and messenger which is the best known battery drainer. I only had whatsapp and gmail. No Instagram, almost nothing. Metal Pro replacing Twitter and Facebook app and even that with notifications turned off. I also turned off Play Store auto update. Add: Even OS update also set to manual. 

What I really get is occasional YouTube notification about LoL matches, few emails from pbb card promotion, and nothing else. Usually on wifi at home.

You can't really blame the OS for battery drain when its doing something behind the scene.

You can opt out if you are unhappy with it. I'm so much happier living without Facebook in my phone.

If you think it's the OS fault, so be it. Android never meant to lockdown like Apple did on iOS. If someone decided to exploit it and yet users keep coming back, who is there to blame. If everyone uninstalled FB then things would change. Would you? LoL... who needs the bloated Fb anyway... lifeless...