Auto-translated
I agree, the interaction with "Hellfire" needs further refinement.
I envision that the demon lord should choose whether to use attacking magic – and then completely forgo "Hellfire," or dedicate all mana to "Hellfire" (whose effectiveness would increase due to the SP boost) and cast Darkness situationally, for example.
Whether there is enough mana for only "Hellfire" or only Chaos needs to be tested further. As does the entire combination of Chaos, "Hellfire," and "Soul Eater." I think finding a balance is possible.
P.S. I'm happy to hear any comments and ideas; I'm not very good at balancing myself.