That sure is one biased comparison if I ever saw one. How about we take their vet 0 performance to compare and not the vet 3 one which obviously favors the Panzer IV because of its armor bonus? Why would you take a relatively rare scenario (all tanks vet 3) for a comparison?
P4 got armor bonus on vet2 IRC? Penetration still the same at all mediums on every vet, with vet only ROF increase.