That’s with auto brightness. I’d put money on he fact that the iPhone has a boost mode in auto brightness as well.This is not right, see the below from displaymate concerning the Note 8.
"it can be adjusted to reach a maximum screenBrightness of up to 728 nits, which is impressive"
Anyways
I have seen the iPhone X display In person for a decent amount of time and I’ve owned many phone because I test them for work...
I won’t say much but I will say that this phone screen is VERY comparable to the note 8. I like what Apple did as far as aliasing goes because it looks VERY sharp even though the “ppi” isn’t crazy the phone is sharp as hell and it looks GREAT. It was like newspaper print on the display it looked unreal. Made the iPhone 8 beside it look like crap. And that 120hz touch driver was also impressive too for gestures.