We doesn’t know that Atlantean metal can pierce thorugh vibranium. If it does nothing can stop Orm.
It can't and that's straight fact. Dumb fanboys like to ignore it and reason that cross universe it loses it's effect when clearly regular ass atlantean steel, YES IT WAS CONFIRMED TO BE A TYPE OF STEEL, is not on par with Marvel's magical godly Uru and the wonderous physics-breaking Vibranium. Uru can cut through Thanos, the same Thanos that shredded the Hulk and crushed the tesseract and Vision's partial vibranium skin. We seen Cap's shield go unaffected by Mjolnir and pierce every type of earthly metal, Atlantis uses earthly metal, it's not from space. Black Panther's claws cut through Arm like a hot knife through butter.