As for my personal opinion, It can go both ways. There is more of a tendency for extraverts to lean towards overt narcissism and introverts, covert narcissism. Extraverts can be extremely selfish and loud about it(*cough*, Esxps, not to mention...). But introverts can be very self-centered and quietly ignore everything that isn't about them. I can't speak for a lot of direct encounters with covert narcissist introverts since it's hard to tell, but narcissism and harmful selfishness I've seen a lot from extroverted types. They literally need to feed off of other people's energy and outside stimuli to stay engaged and motivated. Introverts don't need to do this.