Sundragon, I think you have arrived at the idea that the Great Wheel is morally relativistic by perverting the definition of moral relativism.
Take a Good act. A moral absolutist will tell you that a Good act is a Good act is a Good act. There is a yardstick which applies to everyone at all times and they may be measured by that yardstick regardless of their circumstances or the environment they live in.
Take an Evil act. A moral relativist will tell you that this act will only be "Evil" based upon the perspective from which it is viewed. So for the actor who commits the act, it may even be a "Good" act; for the direct object of the action, it may be an "Evil" act. Moral Relativism allows that an act may be both "Good" and "Evil" simultaneously, and perspective is paramount in the judgment; therefore a knowledge of the perspective from which you view actions will help you understand why you think a particular action is "Good" or "Evil".
Sundragon, I, like you, am rather unsympathetic to a relativistic philosophy because terms lose their meaning: when an act can simultaneously be both "Good" and "Evil", what real meaning do those descriptors have?
But note that moral absolutism is more concerned with the existence of a concrete, unchaning, and universal yardstick to measure the morality of actions than it is with the idea of cosmic justice and "correctness". Evil may still be powerful and vie with Good while remaining pure and unrepentant Evil. The Great Wheel does this: there is a clearly defined TRUTH that Evil is Evil, Good is Good, and while it is possible to changes places by falling or by being redeemed, it is not possible to simultaneously be a Solar and a Pit Fiend.
I don't know what you mean by "correctness" when you refer to Good and Evil; moral absolutism doesn't tell you what is "correct": it tells you what is Good, Evil, Lawful or Chaotic. The individual will then be free to choose between then as their own personal morality dictates. A Good person will generally act Good; an Evil person will commit Evil; a Neutral person will have a smattering of both.
But nowhere does it say that because Good is Good that is should be able to eliminate Evil; there is nothing to say that because Evil is Evil, it shouldn't also be powerful. And "correctness" has no meaning in a moral context, even an absolute one. An act is not "correct", it is "Good", "Evil" etc.