Celtic references in lore

[Yuriane]

all the Irish mythology references are mostly evil/bad things.

They aren't all really evil persay, or at least they weren't always evil. Most of the Celtic Mythology is used in the Voidsent who were at one point no different than us, some even being Warriors of Light, but were corrupted. It might not have been the intention of the devs but I reckon that nicely parallels how in real life Celtic mythology was corrupted by the Church to be either demons or saints instead of gods and spirits.