This is probably gonna sound really dumb, but I always viewed extremes as "midcore". Like, it's not necessarily hardcore, but it's challenging enough for players who aren't casuals but also don't want to dedicate the amount of effort savage and ultimate require. Like, the level of challenge I'd expect from a single player RPG as opposed to the safe roller coaster ride that the MSQ duties offer.
And that, from my PoV, is something this game is lacking more than anything.
Speaking as someone who started playing in 2.3, I used to have the impression that there was a small gap in difficulty between MSQ dungeons and "hard mode"/"extra" dungeons until Stormblood happened. After that came Normal Raids, again until Stormblood happened and turned them into what are essentially more Trials (not that the non-savage raids became easier, I don't think they did, but they're just trials, no mini-dungeon or gauntlet turns anymore...). After that came Extremes, which thankfully are still a thing. And beyond that, Savage then Ultimate.
But the gap between extreme and savage is a lot bigger than expert roulette -> endgame extreme. I'm sure many will disagree but I feel like in this game the endgame focus is always either on very casual content or very hardcore content. If you're not big on either you're left with grinding the same few extremes over and over.
I suppose CLL and DR count as "midcore", but the problem is Bozja also attracts a lot of casual players. Some which don't want to do their job basics well and make the experience super frustrating. Which is why me, personally, I think doing alliance-sized dungeons as midcore challenges was a terrible idea. Coordinating 30+ players, half which learned in their previous 79 levels and 100+ hours up til that point that the game doesn't punish them for not putting minimal effort. Because at the present XIV does a very poor job at teaching players to be prepared for content that doesn't hold their hand. But I digress. The point I want to make is just that there is a whole tier of players in between "casual" and "hardcore" that don't have much beyond extreme trials.