The iron blood warriors were also elite troops of ancient times and possessed great intellect. Their slumber over tens of thousands of years had severely weakened their souls, and they were an inch away from death. The human body alchemy had woken them from their slumber, but also rendered them slaves of Imposa.
Saleen's Eternal Control rules, in comparison, kept the intellect of the ancient warriors intact, allowing them to have thoughts at rudimentary levels. Human body alchemy on the other hand, turned them into complete puppets with self-awareness.
The iron blood warriors were incredibly precious, but Imposa was willing to have them self destruct all the same. It was just so that he could get his hands on Saleen by killing off the elemental creatures covering Saleen's escape.
