Crackpot Theory/Idea

[Iscah]

our world,G'raha's old timeline ravaged by the Eighth Umbral Calamity and the World of the Unsundered inhabited by the Ancients

travel to the First and use its version of the Crystal Tower to create two parallel universes by traveling to both the World of the Unsundered and G'raha's timeline and linking those Crystal Towers located there

all three timelines ... all three Crystal Towers

Where are you getting this part of the idea from? There is no indication that the world of the ancients exists as a separate parallel timeline – it is simply the past of our own.

And we never took the Crystal Tower to Elpis, but travelled through a portal that somehow uses the time-travel device in a different way and does not require G'raha's approach of uprooting of the entire structure to travel inside it.

Also, the First's Crystal Tower (relocated from the future of the 8UE timeline) is the only one that possesses time travel capabilities. The present-day tower in Mor Dhona is a big aether battery with a voidgate generator, but none of the modifications made by the Future Ironworks. Likewise, the present-day tower in the 8UE timeline is in the same state and additionally still occupied by sleepy G'raha for the next 200 years.