While I acknowledge that there are more passionate players than others, I never liked the expression "hardcore gamer". To me, it borns from insecure people that were traditionally made fun of for playing videogames, And when video games started to become more mainstream and popular, they were sad and angry because their beloved and exclusive hobby was being invaded by "inferior" people that "didn't understand what it was all about". So, they started calling themselves "hardcore" in order to make a clear distintction and to claim themselves as clearly superior to those filthy casuals.
That's why I never liked that term. I don't need to use a "title" to feel "more" than anyone. I like video games. End of the story.