I see them as Fallen only from a lore perspective. As for a game design viewpoint they are a new race. Beyond the Darkness/race 5 adding new enemy factions outside of corrupted versions of what we are facing seems odd to me. Not that fighting the same enemies gets dull at times but beyond race 5 it seems weird if suddenly a new race just appeared that was such a threat that the others were put to the side. Personally I see the Destiny universe in its twilight phase or last stand. Everything alive now is just what’s left or what has conquered everything else. We are making that last stand for the continuation of life in the universe verses the Darkness or domination of the Sword Logic. It would just seem so strange to eventually fight the Darkness and then have an oops moment when a new race of beings arrive and they were somehow more of a danger or threat than the Darkness itself? Could one imagine in D3 beating the Triangle ships/race 5 and having celebrations to only have Squid creatures just show up and wipe out everything? As in they would have defeated the darkness as if it was a minor threat? It would have made the entire closed system of Destiny’s story futile and almost meaningless. Like the Traveller and the Darkness were just snotty fighting siblings and then mom and dad come home...