However, this "cost theory" is made and developed by players. Nobody knows if zanz uses such a theory. I only know that there are "elemental bonuses" because zanz has mentioned that in chat (like +atk/-def for fire) . All other rules like "+1 atk per 10 " are guesswork.
3 details:
1) Cost theory is a quantitative model of balance. Being made and developed by players is not a problem since balance can be evaluated.
2) The elemental bonus do not appear in the most recent version of the theory.
3) I believe* it is fair to say that Zanz uses a more intuition based balancing method than the analytical cost theory method.
*Believe based on a response to an interview question.