I can not read that paper only the abstract, so I cannot confirm or deny what it states without reading a convincing demonstration.
As for the first message in this forum’s topic - As I said, the formula that “confirms” the paper is:
Assumes a drag coefficient of 1. Tests on parachutes exhibit coefficients up to 1.7, while autogyro rotor data I linked somewhere else are 2.0 which already indicate a 8/27 power potential. And since an autogyro rotor in parachute mode is showing a counter example of an actual lift-based pumping system which contradicts the paper claiming a theoretical 4/27 limit I see no reason to take an abstract of a paywalled paper as a proof because it is proven wrong.