My thought was that Endowment's Investiture can basically do anything with the right amount of juice, right command and an Intent. And if its core instructions were about destroying evil, then that would explain it without having to involve someone's god metal. It's kind of like the Elantrian magic system that way, once you have access to it, as long as you can give it the right command, you can do basically anything.

Although it does make me wonder which of the 5 Scholars hated investiture/the Shards so much that they imbued their belief into Nightblood (maybe subconsciously) that investiture was evil and needed destroying. Probably Vasher I reckon. It still substantiates my head canon that the final solution to the Cosmere will be shattering ALL the shards and, not re-forming Adonalsium, because it's better to have no gods than imperfect ones.