Just how responsible for the Flood of Light was Hydaelyn?

[LindyFelmenia]

Oh right. Where was this info from?

Those 2 quests:
https://ffxiv.gamerescape.com/wiki/L...w_Walk_with_Me
https://ffxiv.gamerescape.com/wiki/L...n_of_Knowledge

For some reason she is called "Cyella" in game. She tells you what happened to her. Emet Selch also confirms what she said in the 2nd quest. He also hints at Igeyorhm's failure over the 13th shard (which is also mentioned in encyclopedia eorzia) and how they changed their approach to rejoining the shards after it.

[Alleo]

What I don't really understand is why Hydaelyn would spend some of her power to stop the flood of light on the 1st shard. From what we know, a flood of light on the 1st shard would actually turn out to be in her interest, as it would make the shard unrejoinable to the source (just like the 13th shard which was flooded in Darkness). This would make it harder to restore the former Star, and thus, harder to unseal Zodiark. Her primary objective (for which she was summoned), was to kill / seal Zodiark after all.

Because she was created to care about "her children"by giving them a future. For me this includes the shards too.

[geekgirl101]

Hydaelyn wasn't responsible for the Flood. It's when aetheric balance tilts so far to one aspect that causes a catastropic disaster such as a Flood of Light, consuming fire, global tidal waves etc. Hydaelyn was responsible however for the sundering of the star and dividing it into 13 shards. The Warriors of Light were blamed for the Flood on the First because they battled and defeated Zodiark and the Flood happened right after, presumably defeating him tilted the Light balance out of proportion.

As for what happened on the first shard the Ascians toyed with whatever they did to it was such a major botchup that that particular shard could not rejoin to the Source. My guess is they discovered after they messed up that they had to orchestrate a catastrophe on both worlds in order for them to rejoin and their first attempt they only created a catastrophe on that shard.

[Rannie]

The last time she spoke to us was when Minfillia went to the first, however she was speaking to us through Minfillia. The last time Hydaelyn spoke directly to us was when we broke the last crystal free that old middy blocked us from and that was in Heavensward. She even told us at the end of ARR that she was weakening.