A couple of things IME: the drawings showing very low positions don't allow for real roads. I always have 2" between my stem and my chin. Any lower is really risky unless you've been down that descent a few times and have all the potholes and bumps memorized. The other thing is that I get a bit of additional speed in the drops position by pulling my elbows under my stomach as far as they will go. In testing that was as fast as the hands-near-stem-elbows-down position plus it's good to have one's hands near the brakes. The first command is thou shalt not get injured. I'm talking about only 40-55 mph speeds, which is all we get around here.
As I read the above, the OP was satisfied that pedaling need add only a few watts to make up for the additional drag. Of course that's the power meter data. If we look at the physiological stress of pedaling at 120 rpm to add a a few watts, now that's significant. Way better to work on position. Though it's nice to know that simply rotating the pedals while coasting to keep the legs functional might actually be more successful in the long run. Just don't lose that draft.
__________________
Results matter