Demon Lord think "Hero" popping out like mushroom is due to "Will of the World" but Great Spirit just says "Do what you want fam, we cool unless you threat the world too."
That line just basically says "World" didn't care about humans. By that extension something else is powering up these "Hero"s which could means a god/goddess or angels that either think DL is threaten the "World" or they just love human too much.
It's not just the Hero.
Even the Saint was boosted with abilities given by some unknown source, which the MC calls as Will of the World.
And it also seems that this John guy is connected to it as well.
As for the Great Spirit, it isn't the Will of the World, but rather she is the Defender of the World created by the Will of the World, who only acts at full power when the planet is at danger.
The Great Spirit doesn't really care what happens to the living beings on the planet as long as the Planet is safe, because protecting the planet is its sole purpose.
As for why the Will of the World doesn't make the Great Spirit go after the DL.
It's probably because of the purpose. If we compare the Great Spirit as a program, then she is most likely like a Anti-program which is made to do specific task and given a lot of power, and attacking someone who isn't supposed to be under her Anti-program would cause system issues.
As for the name "Will of the World".
It's something MC calls for now, so what it actually is, is unknown.
It might be some Angel like being or a Admin/God like being or even maybe some Programmer if we consider the Whole World as something which exists in a Virtual World, and all the Characters we see are NPC's with set story paths like a Novel, and MC acting against the Set story like a bug, so the Programmer is trying to remove it (kind-off like "Guy" from the Movie "Free Guy").