Responding to the original idea, i.e. How To Make the Leviathan Storyline Better.
I believe two things would be vital to achieving that. First, Barnabas should have been a reluctant slave to the Leviathans, so that he'd be struggling with them and many of our heroes would be striving to save him. Second, the Leviathan Kid should not have been a total absolute jerk. There was, I believe, an enormous potential for pathos in the story of Jeb, a man who was not a man yet perhaps longed to be precisely that. Yet as originally portrayed, one could not help but wonder what super-masochistic, self-hating streak did Carolyn possess to even date this guy, much less marry him!