To disprove the current explanation all I need is a single phrase.
A vehicle power only by the wind driving in the same direction as the wind will be 100% efficient when it is at same speed as the wind (possible only in theory) and from this since no claim can be made that above 100% efficient device was ever proven higher than wind speed is impossible if powered only the the wind and no energy storage.
I think this is at the heart of the problem. As I understand it, your claim is that if Blackbird is travelling faster than wind speed, then for every joule of its kinetic energy taken by the wheels, only about 70% of that energy is returned by the propeller, so the vehicle will slow down until it is travelling below wind speed, and therefore could not exceed wind speed unaided.
The flaw with this argument is that it is not taking account of frames of reference. The wheels are extracting kinetic energy from the vehicle in the frame of reference of the ground, so the number of joules extracted by the wheels will match the number of joules of kinetic energy (with respect to the ground) that are lost. The propeller is imparting kinetic energy to the vehicle in the frame of reference of the air, so the number of joules provided by the propeller (less transmission losses) will match the number of joules of kinetic energy (with respect to the air) that are gained. The gain in kinetic energy with respect to the ground will be greater than this, and can easily be greater than the amount originally lost, even with the transmission losses.
A thought experiment may help to clarify this.
Imagine that I am a passenger who weighs 70 kg, seated in an aircraft cruising at 200 m/s (about 450 mph). Suppose now that I stand up and walk forwards along the aisle at 1 m/s (about 2.2 mph) with respect to the aircraft. In the frame of reference of the aircraft, I have increased my kinetic energy from 0 to 35 joules (mv
2/2), and that energy has been provided by my muscles. However, when the same event is viewed from the frame of reference of the ground, I have increased my speed from 200 m/s to 201 m/s, so I have increased my kinetic energy from 1,400,000 joules to 1,414,035 joules, a difference of 14,035 joules. No laws of physics are being broken, because the aircraft engines had to work a little harder to maintain the aircraft speed while I was accelerating, so they provided the additional 14,000 joules, to add to the 35 supplied by my muscles.
What you are doing in your explanation of Blackbird, is the equivalent of the ground observer in my thought experiment, thinking that my kinetic energy in his frame of reference can only have increased by 35 joules, because that is how much energy my muscles have generated. So he concludes that if I started with 1,400,000 joules of kinetic energy, I can now only have reached 1,400,035 joules. Therefore my speed can only have increased to 200.0025 m/s, or 0.0025 m/s with respect to the aircraft. The ground observer can see that this is obviously wrong, and so there must be a flaw in his reasoning.
Now imagine if Blackbird plus driver weighs 200 kg, and is travelling at 11 m/s, with a 10 m/s tailwind, both with respect to the ground, so Blackbird's speed in the frame of reference of the air is 1 m/s. With respect to the ground, Blackbird has a kinetic energy of 12,100 joules (mv
2/2). Suppose that the wheels now extract 1,000 joules of this energy, reducing the kinetic energy (with respect to the ground) to 11,100 joules and therefore the ground speed to 10.54 m/s. With respect to the air, Blackbird now has a speed of 0.54 m/s and a therefore a kinetic energy of 29 joules. Suppose that the propeller, after losses, manages to add 700 joules to this kinetic energy, increasing it to 729 joules. The speed with respect to the air will now be 2.7 m/s, so the speed with respect to the ground will be 12.7 m/s. This is greater than the starting figure of 11 m/s. So Blackbird can indeed accelerate beyond wind speed without breaking any laws of physics or requiring energy storage.