True narcissists are a kind of anti-social personality disorder people (a lot like psychopaths and sociopaths - they are often intelligent, charming and insane) devoid of empathy, they're true definition is the unbreakable belief that they are the best at everything and they like draining people's happiness by abusing anything they can so they'll feel superiour (arguing that what they do is wrong will only make them laugh at your frustration and possibly try to abuse more as empathy holds no meaningful value to them as they see it as a weakness). They fake emotions, lie effectively and manipulate so they'll feast on low self esteem victims and/or get what they want. They feel only a few actual emotions as they can often experience positive ones with negatives such as anger and envy. They believe they deserve special treatment, anything that challenges their beliefs is an instant threat and they quite carelessly and deludedly continue to lie infront of a judging audiance that has long abandoned the idea of them being innocent. They crave attention, feeling of superiority and anything inbetween. They control people with fear and delusions. Nothing they do is ever their fault in their eyes. A good example of a narcissist evil genius is The Riddler from Batman. So, yeah, being a sadist is a characteristic of a narcissist. The word "narcissist" comes from Greek mythology as a character named Narciss obsessively stares at his own reflection on a lake.
I find comparing a Zed main to a person with NPD (Narcissistic Personality Disorder, where a person holds at least 5 out of 9 personality traits linked to it) holds some comidic value.
TL;DR: Being a sadist is a characteristic of a narcissist. Zed mains can be overexagurated to having a narcissistic disorder for comidic value.