There is no reason to deny that Jesus's death was a historical event, but the Gospel accounts contain difficulties of timing and place, bias toward the authorities, both Roman and Jewish, and items like the torn curtain, which place the Gospel description outside of historical, descriptive fact. The aim of the writers is clearly to try to tell us something, not to prevent us from knowing something else. Those people are still assuming a third-phase basis for words, which is not the Biblical basis at all. It is also clear that the writers of the New Testament preferred it that way. Frye's point is that myth makes a present reality, which is the reality that moves people.
Historians are free to do their jobs, by their own criteria.
So should myth-makers be. I do agree that integrating the knowledge from each discipline is a task that Frye leaves to the readers.