Of course, as mentioned already, not all protein is absorbed. There is competition with bacteria.
The errors fall in assuming things such as:
A) Not measuring a higher protein synthesis rate in muscle in the few hours after consuming one amount of protein vs a lesser amount proves that the balance was not absorbed
B) Not measuring a higher protein synthesis rate in muscle in the few hours after consuming one amount of protein vs a lesser amount proves that there no benefit of any kind would be seen long-term with the higher protein consumption
C) Assuming that there is a sharp cutoff such as that while the first 20 g are absorbed efficiently, anything after that is poorly absorbed.
Or going back to the previously-mentioned Darden:
D) Assuming that if the body is in nitrogen balance over a short period of time as closely as can be measured (which is not terribly closely) with a given moderate protein intake, therefore anything past that must have no long-term benefits.