Dragon God is the most powerful creature in the game, probably in the entire series. There is a reason you don't fight him directly and even his breath can kill you. He makes Midir look tame.
That's not how I see it. Dragon God gets literally taken down by two ballistas that anyone could have fired (but the soldiers were too late). You simply zig-zag until pressing two buttons, and that gets the God to its knees, waiting for you to come closer and finish the job. He's like Seath; maybe impressive lore-wise, but an actual pansy when fought.
Dragon God highlights one of my biggest issues with Demon's Souls. It features some of the easiest bosses in the franchise, some as disappointing as part of the Arch Demons themselves.