This is a simple version of the "if it affects your life" argument for defining disorders, and I think all would agree that someone so narcissistic that it would kill them have a situation which must be treated much more seriously than someone who is just self-centered in a way that makes them a successful asshole (I would place many successful businesspeople in this category). These are of course fluid, and I think describing them as self-centered and lacking empathy is fine enough to avoid utilizing a word I've been convinced is unnecessary and possibly ableist