The Reasoning behind The Sundering? (*6.0 Endwalker Spoilers*)

[Veloran]

Yes tell Xande and Amon, both individuals who would love to find out and exploit Meteions Song of Oblivion.

As I said before, such a situation could easily predate Xande and Amon. Alternatively they could simply be deposed.

Where was his aspect stated?

Did you miss the part where he was going to set the Ruby Sea ablaze, and screamed things like "YOU SHALL ALL BURN"? He was definitely not a water Calamity, not that he was one at all. And they did clearly miss it because of that, insofar as they could not discern the cause of a very widespread phenomena due to being ignorant of the nature of Light. They did recognize the thinning of the aether itself however.

And what of the Seventh Umbral Calamity, where Warriors awakened to the echo by Hydaelyn and blessed with her power fought to halt it?

Hydaelyn never told anybody to stop the Seventh Umbral Calamity. Again, we don't even know for sure if it was her awakening people's Echoes at that time. As I said before she was a non-entity in 1.0.

Black Rose won’t be in any history books, because it was stopped. Ultima didn’t go on to cause destruction, because she was stopped by Hydaelyn and the Zodiac Braves.

Black Rose will most certainly be in history books, yes, it was a big deal. And aside from the fact that Ultima was summoned by a Warrior of Light, she too was not a Calamity. Remember that the Near Eastern Zodiac Braves that appeared before a prior Calamity and those of Dalmasca are not the same groups of people.

That can hardly then be considered Venats decision then can it.

As I said, it may be Minfilia was specifically told to do it, and if not it would still have been a decision made due to melding minds with Venat. This is not similar to Krile's situation, Minfilia literally lost her body and joined physically/spiritually with Hydaelyn.

And it backfired, Venats decision to trust in the WoD worked, until Ardbert accidentally tempered Mitron.

It didn't backfire at all, it went exactly according to their plan and infused the First with huge amounts of Light. They didn't actually want a Flood, that was a mistake yes, but all of the WoDs getting crystals to (little f) flood the world with Light was precisely what they wanted, and they couldn't have achieved their ends had Venat not played into this.

I’m sure she knew down to the exact amount how much energy a ship going to the edge of the universe would require.

She knew the distance and the ship was a construct of team bunny, her servitors. NASA knows exactly how much fuel it takes to get a rocket they designed to the moon, so yes she should have known how much it would take. This was certainly not something worth screwing the First and killing Minfilia over, if she needs more energy later she can just take more, not to mention all the power she was saving for her Primal form which was only used for a backup backup backup plan to commit suicide-by-WoL.

This is not true. The First listed towards Light naturally, due to the fall of the 13th..

That doesn't make it primed for a rejoining, that was only accomplished through Venat and the Crystals of Light. Not to mention she gave WoL SIX at the same time, to the point even Elidibus is like "Zodidamn this is WAY too much Light, I've got to get rid of you before this pops off or everything is going to get wrecked."

Still I will of course admit that she wasn’t truthful here. Much like Emet, Graha, Urianger, Minfilia, Ysayle, and Estinien we’re also not truthful with us on at least one occasion. Do you take them at their word?

There's a difference between "being untruthful" and "killing one of your friends for the purposes of feeding you a pure propaganda lie while framing it as the absolute truth of the world".