FD, Now try deliberately sideslipping the aircraft eg cross controlling on an approach - put left pedal in to hold a heading 20 degrees off your line of approach and which way will you have to move the cyclic to keep flying the approach? Yes... to the right because your rotor disc is trying to flap back along the axis of your travel and has produced a LEFT roll relative to the fuselage.
I agree that a slab sided fuselage will tend to increase drag when presented to the airflow but not enough to roll the aircraft into a turn (maybe 1 or 2 degrees AoB). Otherwise, if you tried to hover in a 30 kt crosswind from the right in your slab sided helo, you would run out of LEFT cyclic trying to oppose the fuselage roll to the right - this clearly doesn't happen.
Some helicopters with more fuselage area forward of the rotor mast than behind it have directional stability issues (Puma for example) but this is going away from the original point of this thread.
Of coures it's easier to fly an ILS in a plankwing, that's why helicopter pilots are so much better (well one of a multitude of reasons really!!!)