As far as unarmed combat abilities, he is on par with Batman(VERY similar backgrounds and martial training). Aside from his sword skills, he is highly proficient with any non-modern weapon he picks up. Now when you put his sword into play, that is where things change. Forged by the gods, Jack's Katana will cut anything that is not protected by magic itself, and was designed to kill a demon lord. As far as tech goes, he does not use it, but knows how to counter a lot of what it can do. I would figure him to be as a powerful threat on the street-level scene of either universe. But where he would truly shine would be on the mystical fringes. His expertise with demons(and the slaying thereof) would prove a great help to any magic user! The only downside is that he is just a human. But when has that stopped him before?