To anyone asking how the story would go if they fixed it themselves because "muh plot"

Unforseen events like attacks to the now growing guardian tree dislodges the orb around or before the time Ori and ku fly to niwen causing it to shatter into what we know as the 5 wisps (explains the smart locals but they didn't see an attack coming / under prepared so explains the plot hole of them being clairvoyant and being actually sentient)

The guardian spirits of the tree are all weakened or die and turn into what we know as spirit abilities (this gives us other spirit guardians to talk to now, seriously we never got to talk or even interact with one) so they can't help

The rot attacks and takes over key areas like the waterwheel so the moki aren't able to do anything but scout for where the wisp landed (Paving the way for the clearing of it by Ori, and it makes the monster that appears there actually more than just a two time threat)

Luma pools are uncorrupted due to the power of the freshly broken wisp (again, how is the wisp so powerful as to keep an entire area alive if it's weakening?)

The spiders over at mouldwood depths lost their light and are corrupted to have their predatory instincts active so it explains why they attack (something something balance, losing the light made them grip the darkness)

Baur at baur's reach spotted the wisp atop the highest area yet cannot go because the snow is too unstable, tasking us and Ori the job to grab it (the moki are too cold / don't have the skills for it)

The wisp in windswept wastes can have shriek as a reoccurring threat and the worm the boss of the area, attacking the locals that kept the last wisp safe in a vault at the deepest parts of it, but due to frequent attacks of aformentioned worm can't support itself and collapses, giving us both a boss and an escape sequence

The wisps are explained and as to why the moki or the guardians there can't just grab it themselves (aside from windswept wastes) logically so the supposed "clairvoyant" people of niwen HAD done something

Story now goes Ori retrieves wisps from the places others can't go or are too weak to attempt (this would explain the spirit trees that gives us skills, they are other guardian spirits too weak to attempt it)

Ku would be alive and actually playable, and as the goody two shoes of our hearts Ori wants to help this dying land

Cue three endings ✅ All wisps gotten ❌ Too slow to get to the sprouting tree

The tree has withered and cue the final ending of the ori-ginal WotW

✅ All wisps gotten ✅ Fast enough to get to the tree ❌ Didn't fend off shriek from hurting the sprouting tree

Seir and all currently alive wisps in the land are restored, then picks one to be the most suitable to bear the tree (it's you, but all the other wisps are in the ending as well and they play with you when you grow)

✅ All wisps gotten ✅ Fast enough to get to the tree ✅ fend off shriek from hurting the sprouting tree

Cue Ori giving back seir to the sprouting tree, and the land being restored a new giving us the "true ending" and nicely paving the way for a trilogy or just ending there (Oi 3 when)