A shortage? Are you serious? (endgame dt spoilers)

[CNitsah]

Disagree with both.
We call a Calamity, when certain events occur. Causing Disaster.
[snip]

then you're just wrong. I'm sorry, it's explained several times in the game, the term Calamity in FFXIV means a precise thing, and it seems you decided to give it a larger meaning. A calamity is what happens when there is a rejoining. The aether coming from the shard renforce a already existing disturbance in the source, making it a calamity. The black rose existed, but the light aether from the first shard made it a calamity, making the poison more potent (far more potent than what the empire expected), since it renforced the stagnation (Black rose made the aether of people stand still). Urianger explains it in ShB. Floods of light and darkness are not Calamities. There is no calamity linked to the 13th, and the 1st calamity ended not happening despite the flood happening. You need a rejoining to have a calamity. You're the one that confusing things, not us.

The Ascians themselves didn't know how to Rejoin the world's. Hence why the Void/13th Failed.

If they knew Dark didn't work EVER. why would they TRY with light(or Black Rose)

This is also false, the ascians did know how to rejoin shards, they did it 7 times (8 in the alternate timeline). It's said in ShB (by Emet-Selch, IIRC) that the first was their first attempt, and failed. But after that, they perfected the method and achieved several rejoining.
And nobody said Dark would not work ever. 7th umbral calamity is a darkness calamity - all the element in their astral alignment. Astral is a the active state, but we learn in ShB that the active state is actually linked to darkness, not light, like thought in the source.