I thought i would share my joy to be playing with this nice camera in ergonomic Nauticam housing!
Since i haven't used other recent Nikon DSLRs underwater i wouldn't be well placed to compare, but i can just say i love how the autofocus reacts in difficult conditions.
Below is a picture i was happy to capture due to the rarity of the fish (scabbard fish i think). which normally lives hundreds of meters deep where i am, sometimes rises close to surface for hunting at night). This encounter was in difficult conditions (1 meter viz at night, he was swimming around me attracted by my focus light beam).
D500 autofocus was spot on the eye though it was quite close (no cropping).