I've never come across anyone who's ever suggested that people with narcissism are neurodivergent in the way it's typically understood. They're certainly not neurodivergent in that context, and you're correct that in no way am I implying that. Narcissism is strictly a personality disorder that manifests in outward abuse and is not under the same spectrum as autism from any interpretation I'm aware of. Understanding it as a disorder and the impact narcs have on others isn't "accepting" it or them, and it's not giving them any sort of excuse/justification for their actions, nor is it extending them any kindness. It's simply a way of bringing clarity to the actions and underlying worldviews that motivate narcissists to act the way they do, which, at least in my case, brings relief and helps elucidate the distinction between actual reality (what narcissists do and what their actions cause) versus the false reality they invent to uphold their ego (what they say they do/are). The gap between those things are what results in the cognitive dissonance that causes much of the pain, confusion, and self-blame in their victims (e.g., they tell you they love or care for you but all their actions indicate otherwise). This is especially important to remember since gaslighting is their primary method to control narratives, redirect things they don't like, and maintain the reality that they want (such as, with their children, having no boundaries).
Conversely, a person working to understand how neurodivergent people think and behave is different because it's an expression of empathy, in order to understand how they are situated within the context of society, norms, and within the broad scope of human behavior, usually with the intent to help them be more accepted or tolerated or accommodated.
Narcissists lack empathy by definition, incidentally.