When I read a description of a narcissist, I think "that sounds like the description of an average human to me".
As we moved into the 21st century, it does seem like lack of confidence has gone away. People are almost "over confident" sometimes.
Is it possible that people are by and large the same, but that social media simply makes it very easy for people lacking confidence to come across as more confident than they really are?
The whole thing is a descriptive generality, defining someone's character is difficult.
Narcissism (NPD) is telling a story to get other people to do what they want. Usually the story they tell is a lie or some form of twisting the truth. For example imagine you ask a coworker how they're doing and they say something like, "Not so good. I just finished a meeting and Bob treated me horribly. He kept talking over me and I felt like I couldn't get my ideas out."
The story seems normal enough. The average person doesn't keep track of what they've heard that is verified and unverified. Say, in this case, the narcissist is not telling the truth about Bob. They're spreading gossip with the goal of getting Bob fired months later, in this slow and subtle way. Worst of all, Bob has no idea. There hasn't been any arguments or any problems between them. There is a high chance he will not know what has happened until it is already over. What does the person with NPD want here? Maybe a promotion or something else that they are likely to get if Bob leaves the company.
Narcissists also use positive emotions when and where possible to aid their stories. Positive roles like being a loved one, a good friend, or a leader are the kinds of roles people question the least. This allows their stories to go unverified, giving them everything they want.
There is a line that connects NPD and ASPD (sociopath/psychopath). Many who suffer from NPD and ASPD have a blend of traits between the two. What both narcissists and sociopaths want is selfish, in that they're okay harming others to get what they want, as long as they can do it in a way that isn't obvious. People with ASPD tend to be forward and obvious and get caught. People with NPD tend to be more sly and subtle and rarely get caught.
I'm not one to usually bring politics up, but Trump is a great example of NPD, because of how obvious he is. If you watch what he says with the lens of looking for twisted truth or outright lies, and look for his motivation guessing what he wants, it becomes quite a bit easier to understand not only where he is coming from but how he works and what his tricks are.