Why is Jack with the Sword of Aeons the first fight?
Jack using the full power of the Sword of Aeons is not only more powerful than he was as a dragon, he was likely the most powerful being ever to have walked Albion.
Unless you are referring to when the Hero of Oakvale fought him.
If so, Kratos walks through this thread.
The only way Jack would really beat Kratos is if it were Jack from the lore, preferably with the Sword of Aeons.