Both Boltzmann's idea of fluctuation and Feynman's argument against it are unfortunately devoid of meaning, because we do not know how highly organized and thermal death universe look like. We never saw and probably never will see another state of the universe and there is no way to experiment with it.

His argument is sound. If there is infinite #s of universes, or the universe keeps reforming infinitely (implication being it will have varying degrees of uniformity), then it's mathematically probable that we would be boltzman brain's in a less coherent universe. We don't observe that.

We don't know whether what we observe is more coherent than the majority of universes, because we have never observed other kind of universe. The very fluctuation hypothesis and the argument against it have no solid basis in science.