In the LN there's a whole little chapter of Guy musing about how it would be impossible for Clayman to controll Milim BEFORE the council even begins. I think leaving that out was a really good decision, becuase it dosen't kill all the tension of the event. We know Rimuru can fuck up Clayman no problem, but this way there's still a smidgeon of doubt if Milim is controlled or not. Though Carrions unbelivably shitty disguise kinda ruins that, but there's not much that can be done about that.