If we tried to simulate a GPU doing a simple matrix multiplication at high physical fidelity, we would have to take so many factors into account that the cost of our simulation would far exceed the cost of running the GPU itself. Similarly, if we tried to program a physically realistic simulation of the human brain, I have no doubt that the computational cost of doing so would be enormous.
The Beniaguev paper does not attempt to simulate neurons at high physical fidelity. It merely attempts to simulate their outputs, which is a far simpler task. I am in total agreement with you that the computation needed to simulate a system is entirely distinct from the computation being performed by that system. Simulating a human brain would require vastly more than 1e21 FLOPS.
The Beniaguev paper does not attempt to simulate neurons at high physical fidelity. It merely attempts to simulate their outputs, which is a far simpler task. I am in total agreement with you that the computation needed to simulate a system is entirely distinct from the computation being performed by that system. Simulating a human brain would require vastly more than 1e21 FLOPS.