I can't quite seem to figure this out. Please let me know if I've got this right: A Mixolydian is simply playing the A major scale over an E major progression. Right? Or you could say that you are flatting the 7th of E major and using A as your root which is exactly the A major scale. So basically mixolydian is just playing the major scale of the IV chord in the key and that's it. Am I missing something here?