Hmm if I deleted Facebook and still used messenger would I gain any privacy or not really? I'd consider doing that.
It's worth noting that the Messenger app requires none of the android app permissions to run. It will happily work with every single one of them turned off.
It also means facebook doesn't get how long you look at each thing in your newsfeed, which is nice. They still get to access all the messages, obviously.
If you want to see what's going on in your friends' lives Snapchat is where it's at.
I don't think they're dying anytime soon, but their obsession with stuffing Snapchat stories into every FB product shows they're at least worried. They will be in trouble if they can't monetize Messenger.