Sorry to bring up this eternal question, but what qualifies as Hardcore?
As far as the industry considers it:
People who think about the game while not actively playing the game, the type of people talking about it in a dedicated discord, chatting about games online in forums, producing media for it, writing guides, seeking to not just understand how the game controls and plays, but really getting in there with the mechanics. The type of people who go beyond just deciding "yeah I like this game" or "nah, I don't like this game" and can really tell you what they do and do not like, why that is, and can then communicate it, the type of people how are putting in more than 21 hours a week into a game (the average gamer puts in ~21 hours a week, or three hours a night). The type of people who take their gaming hobby as a serious hobby and not just something to pass a bit of time and forget about it, and are really keeping up on the news. The type of person who is likely to have a nuanced discussion about hit zones on an enemy, and who have builds that are in the 95th percentile of minmaxed optimization and didn't do so by copying some build they found online, but built it themselves and uploaded it for other people to copy instead. The type of people who will have lore discussions online. In other words, fucking nerds.
The divide between casual and hardcore is more or less that of someone who has gaming as a part of their life and something they really care about and enjoy doing and seek to improve at and get more from as a hobby while discussing it, and those who don't.
Being hardcore with a hobby isn't so much about the impressiveness or difficulty of the accomplishment, but rather how you approach the hobby. There's also the river theory that very rarely shows up in design circles.
There is also the "river theory". The idea of the river theory goes something like this, and applies to table top and video games:
When someone steps into the gaming hobby sphere they will start at their point of access, the game that first really grabbed them. From there they will get swept down stream into more complex and niche titles until they settle out at the spot that they are naturally suited to and only progress to more complex or niche titles once they really need more from their games, but for the most part they will keep moving towards more niche and/or complex titles very rarely less. If the point of access was too far down stream, they are more likely to bounce off gaming entirely without someone there to help them find the right game than they are to seek something simpler or more their speed, in these cases it might take a few blind jabs to get the right point of access.
The average person will enter at something mainstream, think CoD, Ubisoft Openworld Game #695821 or the most recent Bethesda Openworld game. They will get hooked and then seek more. Starting with either popular mods or popular alternatives. Eventually they will try other games and narrow in on what they like, seeking games with more and more depth to them, they will be honing general skills why looking for things that are ever more like that specific thing they are looking for. This is where they tend to learn the names of studios and get to recognize A/AA niche publishers who focus on a certain type of game. Generally after this they get into an ever more specific niche, its like the river branches off, but they continue it down regardless, taking certain branches as they go. The only time they stop narrowing in further on a niche or something more complex is if they jump niches, then it is like they jump back to that big main river and went down a different series of branches, often something closely related to other things they enjoy.
The most important thing for people like journos to remember though is this: Casuals don't replace hardcore gamers, they turn into them. So you sure as fuck better be ready to appease them when they convert, as the hardcore guys are the ones that actually bother reading gaming news and getting involved in any of the discourse. Don't get your meal ticket angry. If you do, you're fucked. I don't care what your activist beliefs are, piss off the audience and you lose your platform because the eyeballs leave and the place hosting it runs out of money, condemning your words to the void. The only place your "important message" will survive is on archives linked to on sites like this.
