If you dare to fight god, gods, demons, phantoms, monsters and even in hell, you're an Arch. An Arch is a fearless warrior and a survivor (prefers death over defeat/never gives in/pain doesn't matter). Someone like this:
And an Angel can be anyone! It just means, is there to help in need. A modern word for Angel would be simply Peacekeeper or Peacemaker. Not every Angel would dare to go to places an Arch would go.
I'm not looking to discuss this, I just wanted to tell you my own experience with this.