Herc's Godhand

So I had a random thought, and please correct me if I'm wrong. Herc's Godhand nullifies any attack below B rank, and it is conceptual, so even if a literal nuke was dropped on him if it was C rank it would do jack shit right?

So my question is, if a heroic spirit had a weapon that was classified as C rank, but it had an ability that makes its attacks A+, what would happen?

Would the attack work, be downgraded, or flat out do nothing?