Callisto over on SpaceBattles-
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-That kind of obsessive rage doesn't come about from a rational thinking process, it comes from a desperate emotional place done for survival, because the only alternative, as far as you can feel in these situations, to that rage is to collapse completely.
Neo I think... is similar to Hazel. They're not really seeking revenge out of a sense of justice or anything... they're doing it because it's the only thing that could keep them going. And Like Hazel, Neo found the first target of her revenge was unbeatable... their choice here was to redirect or collapse, and in both cases, they clung onto a alternate target to shift their rage too offered by the unbeatable primary target themselves.
And that works for a while. It gives you something to keep you going, gives you a focus. But it can't last forever, eventually something will happen that will make you face the facts, and then suffer the collapse that you merely delayed, because rage can never actually solve your issues. Hazel eventually got too much proof that his focus was a pure coping mechanism on his part and his response was to suicidally sacrifice himself for others he had come to care about.
But for Neo... that wasn't an option. Maybe it would have been, eventually, had she stayed in Remnant, I could see Wyatt's talking her out of her rage at Ruby just for sheer sadistic pleasure at seeing Neo break from it... but alas, instead she fell into the Ever After... where she got nothing. She spoke to no one. She got support from no one. She had nothing at all apart from her rage and a power up to help fulfil it.
So that's what she did, she threw everything she had into killing Ruby, and she did it in a horribly sadistic way too... and then she found what happens next, that rage and it's fulfilment still does nothing to solve the underlaying issue... which for Neo, is despair at losing the single most important thing in her life and (and this is SERIOUSLY speculative) that she still blames herself for his death. If she'd been there, she could have protected him, but she wasn't. And why wasn't she? Because she got cocky, did something stupid, and was thrown away when Roman needed her the most.
And the rage she was using to hide herself from that just got taken away with Ruby's death.
It's no wonder she collapsed. Anyone would have done.
Or maybe I'm just reading far too much into a character that, if I'm honest, was only ever a cool character design and little more.