If you don't play as Nimue, there will be few summoned creatures, and they won't be able to absorb much damage (at least that's how it was before patch 3.1), and the orcs will replenish their own damage again with a counterattack. Given the weak defense of the demons, it will be easy to kill the summoned creatures on the way to the original units. As a result, Garuna will significantly increase her attack power, and the orc units will be able to kill the demons with a single blow. Garuna herself is an average orc hero, but she performs very well against demons.