It might be worth noting that Final Fantasy does have a canonical explanation for how the game universes exist in relation to each other, which XIV has stuck to in a few places, and the XI event isn't broken by.

Essentially, every FF game exists as a separate universe within a multiverse, between which is the Void/Interdimensional Rift (the games differ on what exactly they call it, XIV goes for the Rift because it's already got a Void). There are governing cosmic figures over this multiverse, but they mostly don't matter except in the Dissidia games, and while it's possible to traverse this, doing so has only been important in one game: FFV, which didn't use it to cross over.

Iroha has clearly unconsciously traversed it; the main figure who's consciously traversed it is Gilgamesh, who's canonically from FFV and whose appearances are canonical to VIII, XII, XIII(-2) and XIV. There is also a Shinryu around (but not our Shinryu, who is different) and some number of Omegas (which might include our Omega). And then you've got Dissidia, where every character is basically a magic clone of someone in the multiverse except Gilgamesh and Shinryu, who are the real deals and just wandered in aimlessly.

I love the FF multiverse stuff, because there's just barely enough thought put into it to have some logical grounding and explanations, but to still have a bunch of inexplicable weirdo nonsense going on.