I challenge the premise of the question. Tobias wouldn't be Tobias without becoming a nothlit. KA gives us front-row seats of his struggle to come to terms with his hawkishness, and how it changes him. Without his predator half, he would have remained merely a poetic, depressed, total wuss. He wouldn't have done anything like the cat-chasing, butt-kicking, swimming, torture-enduring, self-sacrificing, merciful, heroic Tobias we all know.
Seriously, who here is happy with MM4 Tobias? He's very much not Tobias, just someone similar with the same name, an earlier, pathetic revision who dies a pathetic--but entirely in-character--death.