I think there is a fine line. I consider myself a casual player (have always been, even all the way back to my EQ days). However, I was always captivated by the more hardcore content. It simply existing added some sense of mystery to the game. In EQ, I knew I'd never get a Fiery Avenger but the fact that it existed gave me something to strive for - even if I never really actively strove for it.
I also believe you need a healthy mix of "hardcore" and "casual" players (and those folks in between) if you wish to have a successful game. The "hardcore" crowd will typically help promote all the cool things that exist in the game simply by walking around in really cool gear or talking about their experiences.
However, you still need to have forms of meaningful progression for all players at all points in the game. If the end-game is all "hardcore" content, your casuals will leave (as they will feel gated by the game and any community standards developed). If everything is easily accomplished, then your hardcore crowd will leave (as they simply chew through stuff to quickly) followed by your casuals (as they will eventually also run out of things to do or get bored).
As it stands, the end-game vertical progression revolves around item level. The horizontal progression comes from leveling other classes, future Grand Company ranks, and Beastman reputation.
Thankfully, the game has added a variety of pathways to go up in item level. Soldiery and myth tokens are rewarded through a variety of activities... duty content still being the most efficient way (but roulette makes that relatively simple).
Right now, it does seem that only time and social establishments separate the "hardcore" and "casual" crowds. The "hardcore" crowd typically will have the social connections to run things like Coil and Crystal Tower more frequently.
I do think that the "hardcore" crowd needs at least one other something to feed it. Something that truly tests their actual skills with comparable rewards. The trick is to making this content both fun, engaging but not "required" to progress in other avenues of end-game. In EQ, getting that fiery avenger would've been awesome, but it was not necessary in order for to enjoy the other awesome end-game content in EQ for example.