I understand what you are saying - my experience is that I end up coasting after about 40 mph going downhill on a compact with 12t and can spin, albeit to the top end, on the 52t ring with 12t. There's no testing aside form trying to go as fast as I can. These are the results. There is no wind tunnel and no electrodes.
No offense intended, but this is a great example of how ways can be found with math to discredit the simple act of riding a bike.
The point they are making is that if you spin a 52-12 you can spin a 50-11 equally as well. I don't understand your math comment but if you are spinning a 52-12 @ 120RPM switching to a 50-11 will drop your RPM to 114.