Instead of talking about imaginary worlds' physics I'd want to ask why Hope thought it was a good idea moving all the cocoon inhabitants from a giant floating ball to another one instead of building some giant cities in that huge planet they have below them. I can't imagine all of Pulse being occupied by giant turtles so I think they would have found a place to live if they tried.
Because if you can name a single thing that Hope does in XIII-2 that isn't hilariously stupid, I will give you a dollar. His head is so far up his ass in that game I can't even.
"Hey trusting a Fal'Cie is a good plan. Not like they tried to fuck us over or anything."
"Hey living on a giant ball suspended in air is a good plan. Not like those can come crashing down or anything."
"Hey it's not like I have friends who can time travel to tell me if my plan works or not! I should completely abandon my father to die old and alone to go take a 1 way trip to the future with this person I barely know!"
Hope Estheim is Etro personified. Cuz Etro is a fucking moron.
"Hey, Caius wants to kill me and has no real reason to go on living! I'll put my heart in him because it's not like he's going to be committing suicide, ohohoho."
"Hey Lightning fucking hates the Gods and spent the last game betraying the ones she worked for! THAT WON'T BACKFIRE ON ME."
"Hey Pulse has been assigned by Bhunivelze to hunt me down and kill me! I'll entrust my Seeress with a Pulse L'Cie for a guardian, and wait for Pulse to randomly decide to make a Fal'Cie that interprets and displays her visions!"
Which opens up the whole can of worms for "Why in the fuck are Pulse L'Cie and Pulse Fal'Cie openly working with Etro, who Pulse is supposed to be trying to kill?"
Honestly the only thing consistent between FFXIII and FFXIII-2 is that Snow is still a douchebag.