Orcs vs. Humans

In terms of weapon strength, an orc is superior to humans. And if you hope to defeat it without using Subdue or Berserk, the result will most likely disappoint you. Slowing and vampirism won't help here, because if the orc uses Chain Lightning, its melee units and cavalry will easily handle the situation. But if you have the Staff of Sar-Iss, as you correctly noted, the orc's magic resistance won't help, which means you can subdue and berserk it without much trouble. Then the orc will be in trouble.