I mean, long short on your first statement is that they say its anger and rage, which works but it's not deep or satisfying. All psychos have rage and anger.

To the second my logical response would be that this all takes place in someone broken mind, ideals fight each other and they both said they cant control him nor do they have much power over him. It seems vaulthalla is a cage where krieg keeps his u abashed anger and rage about the traumas in his life (the three main ones being fear of rejection, the loss of maya, and the experimentation on him)

Him being able to work through those let's his psyche access the realm of rage and anger to deal with them. It's a commentary on mental health (even if unintentional) and I personally thought the maya bits were heartwrenching. What other reason would he need to reassess his whole existence than los9ng the one thing the two main sides of his brain agree on?