but my GC told me
since the material uses to raise the grade will be gravel and stone dust,
so,
there is no need to worry about covering properly flashed plywood
sheathing with
this patio base material since it will not retain water. Is he ****ting
me or
what?

Yes, he's wrong. You generally do not want to put wood underground without
an effective moisture barrier. If he can't do a simple thing like this
right how well do you think the rest of the job would be? Get another
contractor, fast.