Well not only does it hit common fairy mons such as the Tapus, and Mimikyu, it also hits rock types like Mega Aero, Ttar, and Terrakion, who would otherwise go toe to toe with Dnite. And yes the ability to hit unaware clefable is nice. (:Sunsteel is really a cool move despite not being STAB and offering bad coverage overall except hitting fairies, and i'm glad those kind of moves appeared in sun/moon. Sunsteel also allows Dragonite to bypass Unaware from Clefable which can be noticed somehow.
EDIT: Iron Head should never been used for Steel STABs or coverage unless you already sketched something else.