I haven't heard anything about the population size of Vi'Zur so it's possible they suffered major losses on an Orc Charge. But I'm also talking about digging in, having heavy pikes and spears that they drop into place for the orcs to impale themselves on. Because I no doubt they could keep going, but that kind of damage can't be ignored by all but the largest and toughest of beasts. It would weaken even those big orcs and the blood loss would take its toll even on those monstrosities. And even without military training, it seems kinda common sense to me. If I am wrong about their knowledge and capabilities, do tell me.