I watched the guy run in his first heat and then in the Semi finals. I will say this. I am impressed that this guy can do what he can with what he was given. He was very impressive to myself and family that watched.
With that said, it sure didn't seem like those carbon fiber feet of his gave him much advantage if any. He placed second in his first qualifying heat, where he raced against 5 no name racers and 2 "did no show" spots. In the semi finals he came in 8th out of 8 and he wasn't even close finishing in a qualifying spot.
I am not sure what sort of proof athletes and scientists need, but there was a good amount of it on display. He was a good medalist in a para-Olympics where he is racing against others with prosthetic legs. When he's racing against other Olympic athletes with feet, he was impressive, but only because he had no feet.
Not winning isn't evidence that he has no advantage. We don't know that if he had real legs, he might not have even qualified for the Olympics at all. His legs could still be giving him great advantage.
The point is, when you've got something like that, it's not a 1:1 competition with other people. There's simply no way to contest that it isn't the same.