The author just dropped the hardest lore bomb in this chapter, it expands and "rewrites" a lot of what we know about Fantasia and magic.
And it shows how dangerous the Mesnie is, if they are old and powerful like that they could very well be the origin of many of the problems that plague the world, but... it feels like besides the Council of 13 most don't know them, which shows an understanding of the power of subtlety from them, which is a scary capacity to such an enemy to have.