I think the problem with declaring FFXIV to be "dark fantasy" is that the very concept of dark fantasy is incredibly nebulous. By some of the metrics I see being bandied around her, Lord of the Rings would be "dark fantasy". It has all kinds of dark elements - a mountain full of dead dwarves, elves transformed into orcs, the Ring's corruption of the soul, and so on and so forth. And yet, LotR is pretty much held up as the template for HIGH fantasy.

ANY fantasy story is going to have its dark elements. Otherwise, there would be no conflict, no plot, and no purpose.

FFXIV does try to include a lot of "human" elements that high fantasy often skips over. Humans tend to be self-interested, and self-interest occasionally leads people to do bad things. Even so, I don't see this as being sufficient to elevate (or would it be deelevate?) the story into the realm of dark fantasy.

To me, a dark fantasy setting has to have a strong element of hopelessness to it. There are heroes, but their victories tend to be minor in the grand scheme of things. That is certainly not the case in this game. The heroes' victories (largely thanks to the WoL) are tremendous, world-altering things. The Garlean Empire was an unstoppable juggernaut, but the WoL wades through its forces like a knife through butter. The Ascians have gone undefeated for twelve thousand years, but in the space of a year or two, the heroes have driven them into a corner. We're so badass, that we have to PRETEND the enemies are harder just to get a decent fight. (See the Wandering Minstrel and his Extreme and Savage encounters.)

The setting has plenty of dark elements, but that's where the "dark fantasy" ends. Things are bad, but they're getting better, not worse. In a dark fantasy, for every step forward, there's typically two or more steps back.