I think it's okay for a few items to not be internally consistent with their respective packs. We have the Dreamspitter (in GH, needs Dreaming Dark) and Gem of Many Facets (in DA, needs Red Fens), and I'm pretty sure there are others.
This weapon is unique, and warrants unique mechanics to support it, including having it upgradeable in a way that other raid loot is not, and having it require loot from other quests to do so.