It does not make sense. What secret goals could MC have if Sister technically won the war on the first day? Why go after some super complicated plans when the MC could just channel their magic on Leon’s forces and destroy them and then just join to Sister.
I don’t have a strong hatred or sympathy for Anta, but I honestly think she’s incompetent because she’s too preoccupied with her paranoia and hasn’t shown ability to look at facts objectively. But I agree, she had too little screen time, maybe if we saw her in moments when she shines, she would not look so plain.