In hof, Dorian and Sorscha talk about iron and it's ability to negate magic (ch26).
What if Dorian needs Manon's Iron to help ground him? Help him control his magic? Just like Rowan's wind and Ice helps calm/aid/help/grounds Aelin.
Also does the iron in the ironteeth witches negate their magic and when they yield it's really them melting their iron and releasing the magic that has always been inside them. Acting like iron bars to contain it.