I am in confusion. You mean reducing(reducing rpm) pitch in a dive creates more drag? When you reduce pitch, the blades are more like feather prop, correct?
Or you mean, if you also reduce throttle, and the engine starts windmilling, that means it is the drag that keeps rotating the engine, and (correct) more drag(but minimal.
(i gess,i am no expert just curious
I think in a dive if you are with limit revs (not over-rev) the engine is slowing you down. Like in a descent with a carr, if you put low gear in, it will slow you down.