Iroha

[Cleretic]

The Rift in FFXIV is what separates the shards of the sundered world. There is no confirmation that it stretches further than that – the closest is Omega reproducing things it has seen via the Rift, but between its inability to distinguish fact from fiction and that "things from other FFs" encountered in Eorzea tend to be copies rather than direct crossovers, there's no guarantee that Omega hasn't simply found either similar copies or legends in the other shards.

Of course, there's the question of just how Omega got the ability to interact with the rift when it was built on an unsundered planet, but it's possible that it evolved the ability after arriving on Etheirys.

It's not clear exactly how this Rift interacts with the other Rift, or if they're even different (much like how the space between Earth and the moon and the space between the Earth and Mars are both 'space'), but both of them do exist. After all, Gilgamesh is more loudly 'the Gilgamesh from FFV' here than he is in most other FFs. And in the English translation, the Kefka minion confirms Dissidia NT is somehow canon.

[Iscah]

After all, Gilgamesh is more loudly 'the Gilgamesh from FFV' here than he is in most other FFs.

Is he, though? As I said, plenty of other FF characters have appeared here as copies of their original-game selves while actually being entirely native to FFXIV's world.

How would you tell the difference between "Gilgamesh who is the actual same character as in FFV" and "Gilgamesh who is a copy of the character in FFV"?