Michael's impression of Spartan was that it was very steady. Other than Jester, it was the only other undead that could pass as human.
However, compared to Jester it was not particularly flexible. Though it could be ruthless, it lacked Jester's extreme mindset, but what it had instead was stability. Perhaps even rigidity.
When Michael had said that the empire's subjects would live if they surrendered, Jester hearing that might either comply as told or find a way to twist the words around if he had his own ideas.
That way he would technically not disobey his master's words while potentially gaining more benefits for himself or his master.
Of course this depended on whether Jester had any other thoughts in the first place. As a bloodthirsty creature, there was a high chance he would simply kill before they had the chance to surrender.
But this also went to show one of Jester's greatest strengths. His flexibility.
