^ yea, theoreticaly/scientifically/mathematicly speaking, you are 100% correct, however as people whom have tried and owned these above have mentioned, on a practical in rreal life situation, your point is mute.
You may notice ythe drag but I'd be willing to bes you would feel more drag from many other issues that will have the same effect on your overall effeciancy on a long ride.
Everything from a big things like lower pressures in your tires to tree pattern, tire thickness aka rolling resistance up to things like aerodynamic's are far more likely to effect your overall ride effeciancy, to just as important things like weight of bike, your hydration and what you have eating to your style of ridding such as many over breaking pe taking less efficient lines, all of these things on there own are properly just as effective at slowing you down as this light, all together plus all the other things I haven't mentioned will have a far great impact on your ride overall than simply the minimal drag from this light.