Everyone makes mistakes. Even the most "hardcore" of players pull an oopsie in dungeons. You know what's great about XIV? It doesn't punish you for failing, and let's you try again. And again. And again.

It doesn't take XP.
It doesn't decrease your level.
It doesn't drop any of your gear.
The repair costs are laughable in this game compared to what they can be in some others.

There is no negative cost to your character for encountering a challenge and failing a few times. It's meant to be fun, and have a small sense of accomplishment for beating it.

Saying that The Dead Ends is 'hardcore' is just absolutely ridiculous. I don't savage raid, but I've watched them being done. The mechanics don't even compare. It's night and day. There's challenge to Dead Ends a bit for the casual player but they are all mechanics a player has seen before. Line aoe's, boss limb lighting up to show the side of the arena that is going to be aoe nuked, growing circular aoe's in order, rotating aoe's that the player needs to slowly outrun... Even the esuna'ble debuffs. Everything here has been seen countless times before, in some form or another, countless times ad nauseum. The only thing that's new is the combination flavor of them.

Asking for a player to have foundational knowledge of the game they are playing, HAVE played for 90 levels up to this point to the veritable end of the story, is not a push for "hardcore". It's literally asking the player do to the bare minimum challenge that one can expect after seeing every other foundational mechanic from the entire journey to that point.