I think maybe the problem here is that we're labeling characters but really should be talking about the worldview of the show, revealed through the characters.

To that point, I'd observe that the show's most unhinged character is also the one with the most humanity and alertness to the world around him. What is the show trying to say about life by suggesting that you'd have to be like Kramer to escape the gravity well of self-absorption around Elaine, George, and, most of all Jerry, the character you're most meant to identify with?