Dawn of Night

After the Gods left, the demons in their Abyss grew jealous of the world they built. All they know is destruction, and have long ago run their Abyss into nothingness. They could not fight the gods, they were too powerful, but these people were weak and ripe for the taking. So they dug and climbed to burst through the darkness, and with them came the dark where they prowled. The gods turned at their creation, and returned once more. Conqost fought them off with his sword, Feos planted the fear of the dark in the people, Innos once again taught them to care for the wounded, and Recos gave them knowledge of the god's own weapons, so that they could defend themselves. They then returned to Elysium and their solitude, knowing that without their brother they were weaker.

Demons raided the material plane for as long as people have records, and the Abyss is a chaotic burbling mess. And of course, demons seem to only know destruction.

As a myth of the Mountainhead church, and a pretty simple one at that, most people at least have a tertiary knowledge of it.

Many versions have the demons coming as a sort of proving of the 5 attributes, with the material plane using them to drive off the demons, no divine intervention needed.

It's pretty simple, so decently well received.
Some people find it insulting that people needed help to fight demons.

There are plenty of murals of Conqost slaying demons, and tapestries of dark coming from below.