I think the Note 8 has better battery life when using the screen for things like video playback but the IPhone 8 plus might have better standby. I'm not sure but that might account for the differences in battery life amongst different use cases.
I’ve used both for video playback, my battery has fared better with the iPhone. Both with high brightness. Perhaps I’m doing something with the Note that I’m not with the iPhone that I’m unaware of.
Standby isn’t close. iPhone fares much better. I think that’s just the nature of iOS vs Android.
However, Note 8 charges like a demon. Both wireless and wired. Wireless charging with the iPhone is so slow it offers no advantage even if you just want to top off.