Warriors of Light question. Explanation needed.

[Lethorian]

That's one possible interpretation, but it's not all that cut and dried. There are some references that could be interpreted as meaning that all our characters, whether legacy or not, were in fact those Warriors of Light that fought at the Battle of Carteneau.

This is what I think. Kind of how the story starts in three separate scenarios depending on what city state you chose, 2.0's story has a similar scenario where there are three separate storylines depending on if you completed 1.0, played 1.0 without completion, or are new to xiv entirely. Even though there are many players in the game while you're playing it is YOUR story and everyone else are just "adventurers". At the conclusion of 2.0's main story it can be assumed that the stories merged together effectively making you out to be a warrior of light, regardless of your starting point.

[Toranja]

The way NPCs use the term is to identify those who were touched by Hydaelin and live up to their destiny. Even though Hydaelin's existence is largely unknown to them.