I also have a note5. Keep in mind that some of the " battery issues" that crop up, are just degradation from being charged hundreds of times. My battery life has tanked as well, but it wasn't from an update. It was from a little over a year of using the hell out of my phone. It's one thing they has me considering a V20.
I know what you mean, hard to know how much of it is due to repeated use. I'd look into the V20 but it is too big for my liking.