Not great.
Artifacts from the set are worn by everyone.
The complete set is also worn by everyone.
BUT! If a hero of a specific race wears the set, they receive additional bonuses in a certain amount. It's not too imbalanced, but enough so that, for example, it makes sense to give the "Elven King's Armor" to an elf hero as soon as possible.
Well, it's simpler, yes - a specific race in the artifact-bearer's army receives bonuses on top of the set's bonuses.
God save us everyone
Will we burn inside the fires of a thousand suns...