IMO

Casual - doing stuff at my own pace, not have to have less playtime because I may just AFk and come back to do stuffs slowly.

Hardcore - spending playtime dedicated to certain content no matter how much time they have and how hard the content is.

For example, I will call my friend who is in Chocobo racing everytime I see him online as "hardcore racer". (insert LoV to be meme)

I do savage but I didn't try to beat God Kefka until few months later after I'm on 360+ then I try hard to clear him, I'm considering myself casual raider.

just my opinion on casual/hardcore.