o be honest, the Occurians already control the world, they already have the power to manipulate humanity, and the Dynast-King is proof of this. I'm afraid I feel you have missed the point of XII's plot if you seriously believe in this theory.
Of course they already achieved they requirements.AND NOT.Why?Because there is a time loop-involved here.That is what I am trying to say.Basically Y(the true villain of FFXII) wanna Cid to create the basis for the Sun Cryst and a ship like Bahamut.Therefore he wanna Cid to fill the Bahamut with the cryst mist and crashed into Rabanastre while killing Bujerbans and the Marquis in the process.That happened on another timeline and it probably affected the weather on the Giza plains raising the water level during the rains.
Rabanastre was then flooded on water and Bahamut would be near the center of the city.The city,haunted by the recently appeared Occurria would change a lot.The moogle teleporters would become more powerful.The city would become what we know as Giruvegan.
In order for the time loop to work,the Occurria needed to "Compress time" so that Cid can travel to the sun cryst.
Cid created little shards of deified nethicite which were still imperfect.When the world was haunted on the first timeline the Occurria haunted these shards creating the sun cryst.
To explain better:
Valendia+Ordalia=Era A(past)
Kerwon(includes the waterfall island)=Era B(future)
1-The Bahamut was filled with the mist of the sun cryst on Era B
2-nethicite is created by Cid on Era A
3-Bahamut got from era B to Era A and crashed with Rabanastre.
4-Rabanastre became Geruvegan.
5-Occuria haunts the nethicites created by Cid and it becomes the Sun Cryst
6-Time passes and era B came.
7-Step 1 happens.
Therefore there is a Time Loop.
The Occuria needed to magically join Era A with Era B through space to easily deceive people(including Cid)
Therefore that thing about defying the Gods is crap to proceed with their time-loop agenda.
To emphasise Wolf's point, Venat speaks to Dr Cid in Archades. There is not a high concentration of mist there. Venat also protects Cid at least once in the game, interacting with the material plane.
Of course it is.solified mist(a.k.a nethicite).
I am not saying they canīt move a little beyond the mist(solid or gas).
Itīs like fish out of water.They keep surviving as long as they didnīt stay out too much time.
Nethicite seems to behave like Alladinīs lamp.Cid and Vayne have shards of nethicite.And Cid meet Venat first on Geruvegan.