Dusk Vigil never actually shoots its Fusillade

Because Ember Fusillade adds a new ember each time it is cast, and only shoots them if none are added for a while, if you are casting constant with Dust Vigil (which you almost certainly would be), it just keeps adding embers once capped (not actually adding them, just refreshing the shoot timer) and never actually shoots them. This effectively makes the unique useless.