BiS chest question

Hey all.

Im looking at BiS pieces and I keep seeing that for the chest piece its “Scaled of the Scheming Behemoth” from Il’Gynoth.

What makes that a better option than “Last Vestige of Neltharion” from N’Zoth?

I assume its because you can get a IP/Natural Harmony and a heart of darkness where you can’t on Last Vestige.