I wouldn't consider myself either casual or hardcore, honestly. I tend to think of "casual" players as those who spend very little time playing games and have very little skill because of it, and "hardcore" as the people who speedrun on the highest difficulty or have well over 1000 hours on a single title. I don't really fit into either category: I play games far too much to be a casual player, and I would consider my skills above-average for my preferred genres so that doesn't match up either. But putting 1000 hours into a game or setting myself arbitrary restrictions to see how good I am? I don't have the time.
Things that people generally consider difficult I don't find especially challenging a lot of the time - Souls games, Fire Emblem's higher difficulties, etc. Any kind of RPG that is generally considered hard, I will probably not find hard. Put me in front of anything more than a very basic level puzzle and I'm useless, though. I also have zero skill for fighting games, and I doubt I'll ever go beyond Hard in Project Diva titles unless I practice some advanced techniques that I probably will not have the patience for.
My appreciation of difficulty is different from most people's, and I have different ways of measuring it. I will often play on easy mode but it's a question of saving time rather than lack of skill - as I've said before in other threads, many developers don't seem to understand that merely bloating enemy HP and making them hit a little harder, or reducing your EXP gain, doesn't change the "grind to win" gameplay mechanics other than to make it more time-consuming to get to a point where you can win comfortably. I'm not going to waste my time grinding to achieve the same results just to prove I can do it. When developers get difficulty right I tend to play on higher difficulties for a challenge, but very few developers do, so what's the point? Playing on harder difficulties doesn't automatically make you a "hardcore" gamer when the gameplay is fundamentally the same, as far as I'm concerned. That there are usually things you can easily exploit to avoid playing the "hard" parts as they were intended kinda defeats the point of it too. I mean, as a random example, you would think fighting the level 120 Avalanche Abaasy in Xenoblade Chronicles Definitive Edition at level 20 would be difficult...until you realise you can topple lock it indefinitely so it's just a question of how long it takes. Anyone can do that. It's not really "hardcore" to do it when the game hands you all the tools needed to do it.
I don't play any single game anywhere near enough to consider myself "hardcore" and I am acutely aware there are people better than I am at the games I do play for longer periods. As a MH player I am way above average in skill level - or I was, god knows what I'd be like after not touching the games for months - but I'm very far removed from those people who can speedrun EX Deviants, and that's not something I would ever want to do. I'm also only proficient in Adept Light Bowgun, and a "hardcore" player would be proficient in all weapon types and styles. I never took the time to learn; I found what worked for me and what I enjoyed and perfected using that. Whenever a game has a ranking system I am immediately put off, too - I have never been inspired to earn the best rank in stage-based gameplay. Unless it's going back to an earlier stage with power-ups I find replays to be extremely boring, and I only tend to learn the layout flawlessly if there is something in it for me. I derive no personal satisfaction from perfecting something otherwise, so I couldn't be considered "hardcore" on that basis. Online leaderboards? A waste of time. There's always going to be someone better than me.
I've always felt like hardcore players treat games like jobs...hell, for some of them, the game IS their job, because there is a lot of money in eSports. That doesn't really sound all that fun to me, and the game very rarely rewards me for doing that, so I don't do it. If there is adequate reason I am all for it - I used to be a crazy trophy hunter, and I spent well over 1000 hours completing my MHGU Guild Card, hunting over and OVER for crowns - but I've found the number of reasons I will accept has grown much smaller over the years. But at the same time, playing games casually holds very little appeal for me - with JRPGs it's impossible, because I've been playing them for years and, my skill level aside, I like doing sidequests. But I will put games down and forget about them, and the kinds of games that I could be more "hardcore" with - MMOs, etc - I just don't have the time for, so I leave them alone.
Basically, I play games how I want to play them, and that varies depending on the type of game. If I'm invested in the gameplay, I probably approach what people define as "hardcore" in both skill and time spent on it, but not to the extent that I'd be speedrunning it or something. If I'm just playing a game for the sake of playing it, I'm closer to the casual end of things, but with more skill than you would expect a casual player to have.