So slight detour from the current topic
The undead are supposedly immune to OG influences...could that be due to the fact that originally the undead are servants of the jailer??
Similar to the Nathrezim who chopped off his horns and became light forged which SHOULD guarantee purification and devotion to the light but apparently he is a double agent.
This means the rendorei will always be the possible servants of the void but are possibly the best weapon against the jailer alongside the lightforged of which we only have 1 soldier and also Anduin who isn’t light forged but does have a strong connection...this same connection could be why Arthas was never a complete servant to the jailer.