The thing I had forgotten was to re-allocate the skill points (after being spliced they all got removed). As soon as I had done that it was real easy to defeat the Chimera. So I'm not so sure if you should make it easier.
By the way, what happens when you press "New Game"? Will a new slot open up or will all the previously stored games be replaced empty slots? I'm afraid to press the button in fear of losing the stored games.