Rowan's army was so massive that a mortal could spend his entire life walking past their seemingly endless rows and he would not be able to see more than ten percent of the entirety, especially for the Spirits and beasts like Vraegar who were so massive they were the size of worlds. Only a battlefield that could cover light years across could hold this army.
When Eva had sent Tenma to attack the demons, she had begun posting everyone to different positions, different members in the army all had their strengths and weaknesses, and sometimes the best way to employ them effectively was at specific places and moments, and she would ensure that everyone here performed to the best of their abilities.