I wrote a long response so it will be a few of these reddit things - (Part 1)

I’m gonna start with your final point which is flat out incorrect, because nothing DESTROYED FF characters home worlds. Their home world is Radiant Garden, they fled Radiant Garden when it became Hollow Bastion and was being taken over by Darkness; they refuged at Traverse Town while Cloud and Sephiroth and clearly Zack back in the day simply traveled to Olympus Colliseum. I have a suspicion that you didn’t beat KH1 because if you knew anything about Traverse Town at all you’d know it’s made up of surviving light-fragments from worlds which have fallen to darkness. The light in people’s hearts occasionally outshines the darkness which consumes their world, and those individuals are transported magically to Traverse Town such as Sora. It was made very obvious due to being nighttime all the time that Traverse Town was itself falling to darkness, representing the last light in the multiverse being snuffed out. The End Of The World is similarly made up of all the other worlds consumed by darkness, hence why you go through each world you’ve already visited throughout the game… THEY’VE ALL FALLEN TO DARKNESS - and as the entire multiverse hangs in the balance, you must now open the door to Kingdom Hearts to shine the light thru Ansem Seeker Of Darkness (killing him) and back unto the worlds in order to restore them along with their population. At the end of KH1 all of the worlds are restored along with Destiny Islands which is the literal reason the game ends with Kairi floating away from Sora as she returns to the sandy beach and Sora drifts back to the Land Of Departure/Castle Oblivion, since that’s where his “heart belongs”, as Ventus is resting there sharing his heart.

The FF characters who were refuging at Traverse Town were all magically transported to where their hearts belong, being Radiant Garden and they have been there ever since. Radiant Garden’s transformation into “Hollow Bastion” was supposed to represent that it had halfway fallen into darkness already, from powerful dark presences such as Braig and Terranort and all of the other heartless experimentalists and their army of Heartless. The FF restoration committee took it upon themselves to start their own organization to save their home world and counter the darkness already present, most notably by setting up those little hologram machines that would roll around and hit enemies; furthermore later on by unlocking Ansem’s study and learning the truth of it all and that it ties directly into Sora’s journey…

Also “useless idiots who can’t keep peace” is a bit harsh… literal darkness is consuming everything it’s not like they are doing politics and treaties, they’re actively under attack all the time searching for refuge in light. Darkness eating worlds is kinda the whole point of Kingdom Hearts up until now; Sora being the one who fights back the swarms and seals the keyhole to prevent more from infecting it deeper (funny that’s not a thing in KH3). If you can’t stand the concept of Darkness Consuming Worlds, on which the very first game was created, how can you call yourself a Kingdom Hearts fan? Please go play and finish the very first game.