My theory is that Jax only believes in character archetypes because Ragatha accidentally told him so in a failed attempt to comfort him in his early days in the circus.
>Rag: Hey, I know you feel bad and that you hate this place, and that you probably feel like you don't fit in, but we all have our places in the circus. For example, uh... I'm the happy one! yes! Kinger is a little crazy, and you... could be... uh... the funny one!
>Jax: *sniffs* Could I be the funny one?
>Rag: Yeah! The funniest guy in the circus!