Why would an archetype help? You will know about the inner workings of your main characters: What motivates them. What causes them to stress. How they respond when they are stressed. What style of dialogue they will use. And most important, how to shape their arc in your plot. When your characters are true to the archetypes that have been used since humans painted stories on cave walls, you will speak to an audience in a language all understand. Your plot can be anything you want. If your characters feel real, if your audience can relate to them, your story will be successful.