How thick should plywood decking be assuming you are using joists 16" on
center?

In my earlier years, perhaps 20 years ago, I worked for a builder who
typically used 5/8 floor decking and 1/2" on the roof and exterior walls.
Now I'm faced with an architect that insists 3/4" on the floors is a must
and 5/8" on the roof and walls is needed.

Does the floor decking depend on the finish flooring. The builder I worked
with would always install wide plank 3/4" hardwood flooring. But when I
mentioned that to the architect, he insisted that I should still use 3/4"
decking under it. His concern was regarding the holding capacity of the
nails for the hardwood flooring and that it would avoid squeaky floors
later.

Any comments?