Weird thing to say, but this reminds me of Path of Exile where the developers admitted to balancing the super hard boss fights around the player being able to log out and save their character with no penalty. When you have the option to completely tap out of a fight and not go back to it, you have a greater luxury of making it hard so that the player returns more prepared and relatively unharmed (compared to if the character was in Hardcore mode and couldn't log out to safety, dying to the tough fight and losing the character forever).
Possibly the fights in FFXIV are balanced around being able to Resurrect and not caring about resurrect sickness, to a point. OFC it's not even like FFXIV allows this everywhere, like Baldesion Arsenal and Savage Criterion.
