I agreed with everything you said until I saw your edit. One of the most disturbing parts of NPD that you didn't mention was lack of empathy, and magical thinking...the grandiosity gap between what the narc thinks of himself and his accomplishments and actual reality of who he is/his accomplishments. They might actually feel inferior somewhere deep down but they are usually not introspective enough to realize what is really going on. Someone with narcissistic traits can change someone with NPD can't.
Narcs (people with NPD or a narcissistic personality...not just some narcissistic traits) can't change any more than someone with a handicap can change that they have a handicap, but anyone who is being abused by a narc will probably try and change them at first because they care about them. It's a harsh reality to accept that someone you loved didn't/couldn't care about you at all and everything about them was a lie. Once you understand that your partner has a mental illness and is dragging you down with them, to keep your sanity and mental health of course you have to abandon them and rebuild your self esteem. But it's hard to abandon someone you care about because usually the mask does not slip until they have their claws deep into you and by then you are addicted to the roller coaster of the idealization/devaluation cycle. Usually people have to recover from this, usually these people end up in therapy it's not a normal breakup. Already mad at themselves for being naive, missing red flags and putting up with abuse, labeling them narcissists at this point is just cruel and not true. Deceiving themselves? Yes. In denial? Yes. Automatically narcissists? No.
You don't think that a partner of a narc thought that maybe they were the narcissists while their narcs were projecting their mental illness onto them? Of course they did. Yes, a victim can become a narcissist as a defense to the abuse...a terrible nightmare for someone that was born experiencing true empathy, but that's not the same thing as denial, and trying to change your narc. At the point they become self-centered, lose empathy, become abusive and exploitative then they've become a narcissist themselves.
This is my last post in this thread. I'm with blueta on this one. It's depressing to think about!
"Battle not with monsters
lest ye become a monster
and if you gaze into the abyss
the abyss gazes into you."