Regarding the state of Okoto before the great cataclysm, I still support the idea that it’s all lush jungle. I think the Creatures roamed all over the island back then. Each represents the aspects of nature that are necessary to sustain the island.
Ikir and Melum are heat and cold, both maintained the intricate balance for the right temperature and climate. Ketar and Terak are rocks and soils, the ground for everything on Okoto. Akida is water that nourish all life. And lastly, Uxar is plantlife that populated the island.
So every Creatures worked “in harmony” to create that all green Okoto. And having all elemental Creatures doesn’t always mean Okoto need to have six differrent terrains.
However, the Great Cataclysm then radically changed the island and divided the Creature, confining and creating niches for the each Creatures instead. Thus concentrating only one elemental energy into each region, resulting in six elemental regions.
And now that the Toa managed to unite all six Creatures again, I think the balance of the island will be restored, and island will finally start to heal itself (if not for the destruction UtD will cause I supposed).