Heartbreaker Dagger Spells have Culling Strike mod doesnt work with Bane

It does work, in that the Bane spell will have Culling Strike.

But having Culling Strike means that if it hits something, it will kill that thing if it's on 10% or lower life after the hit. That's fundamentally what Culling Strike is.

So because Bane can't hit anything, it having Culling Strike is entirely irrelevant.