I agree with that. The main reason why Kyrie killed everyone has to be the most obvious one: It was the best thing to do in the given circumstances. Any other motive, especially an anti-hero one, would be kind of a disappointment, considering Kyrie’s extremely rational & selfish personality.
I really like the idea that she didn’t mean anything she said about Ange, and the reason for that was to manipulate Eva into taking Ange’s custody. This TP made me really hate Kyrie, but this theory makes her actions at least understandable. If only she chose to give Jessica a quick death instead of mutilating her in such a gruesome way (and boy, that was brutal…) , I would’ve hated her even less. But if she didn’t break her rifle on Jessica’s face, she would’ve won, only because Eva was so hesitant.
Another reason why I love Eva so much. Don’t get me wrong, the fact that she didn’t shoot Kyrie on sight could’ve been her demise, but that only proves how good of a person Eva really is. Behind the mask she wears in the presence of her siblings, she’s a benevolent mother who would become selfless for the family… She cared just enough about Kyrie’s motive, about the explanation, that she ceased to prioritise basic survival instincts that would give her the upper hand. So much that Kyrie even had the chance to point the gun at her.