Edgar knows that, at this moment, an Ares is weaker than he is. But that brought him overconfidence that made him lose. Still, Ares would have used dirty tactics to distract him, e.g. badmouthing Diana.
I still do not understand how much of Zarathos power he is using. At 100%, he would have the power of a nultiversal being such as Michael and Lucifer. But what percent is Edgar using so far in this story?