A Kompa can even kill a group of leprechauns!
A human can dispel all illusions with a dispel charm or a dispel spell, and as for the arrows... how much damage will 30 damage do in the final stages? 450 damage from an arrow... heroes usually have resistance (at least those within range), and if you encounter resistance in units, you might as well raise the white flag.
I haven't played against a human on difficulty 4 and don't even know how, so I can't judge how to play against a human.