I'm not starting from a 100.
If I start from a 100 I would lose nothing without the watch paired and 1-4 with it paired.
I agree that something is running. I can't find out what though. Even dfu restoring the phone, setting up everything as new, including the watch and using a new iCloud account does not solve the problem. And the weirder thing is that it happens on iPhone 6, 5C and the 7, but not the SE. Have you seen my screenshots? It's easy to see what I'm talking about.
I am pairing the watch anew again right now as per your suggestion, maybe I get lucky this time. I have met more people in my environment with the same issue. They could solve it by disabling Siri, however. Disabling Siri makes no difference here, but it does make a difference without the watch.
To be clear; I have Siri completely disabled (even though it still shows up in the battery list, I guess for dictation). Background refresh also, push notifications as well, and almost no location services.