"Why use magic, if they have swords?"?
Because the first attack should be magical, just in case the monster us far stronger than it looks. Both the Impation and Dragon can attack from afar and dwarves full grown humans easily.. And obviously can kill any man in a single hit.
During the middle-ages; the world was engulfed in sheer darkness as has never been seen again. While we know some of what happened; there's no one to tell how far things went between man and monster... The sacrifices, pain and betrayel that goes on even until this day!