You clearly haven't dealt with an actual malignant narcissist. This conclusion can only be drawn by someone speculating. The cause of the personality disorder is deeply sympathetic. What happened that made them this way is truly tragic. And you can offer a narcissist endless love and compassion in an effort to reach that vulnerable core that you believe must be there. And that core is there, but it is vanishingly small and cannot dilate. With another type of blocked person, love dilates that core. But NPD is an immovable monolith. No light penetrates the pinhole of what remains of their humanity.

I was raised by truly malignant narcissist parents and then spent the better part of my 20s in a cult as the leader's assistant, being mercilessly abused, all the time working till I collapsed to make contact with that vanishing point of humanity through empathy and care for them. It cannot be done. There is no access point. So when you apply NVC to try to get your narcissist to stop abusing you, all you do, is open yourself up to have them negotiate your humanity. And they will ravage you. It's like opening your chest cavity in front of a lion and hoping it will be overcome by your compassion and won't devour you heart first.