Well that seemed unnecessarily antagonistic. Points for prose though.
I'm expecting Miranda's 'Magic Items' to make a show rather soon. Something about that increased magical energy. And, while I would like to see Miranda die so the Deegan's don't have that 'I Win' button (Plus that would set up some serious credentials as a Badass I think), I don't think this trick was as much of an ass pull as you'd suspect.
Firstly: He stated that he'd rather Miranda follow him willingly. For whatever reason, we don't know, maybe the magical fluctuation gave her enough power to keep him from enchanting her? Keep in mind, when she tried to cast a very basic spell on the Planar Crone, she wound up causing a tremendous explosion due to the magical fluctuations. Maybe it kept increasing? Who knows?
Maybe he's just a damn racist that thinks the Circle should be all humans? (A racist villain wouldn't exactly be a shocker.)
Then there is the point that illusion magic is not merely visual. Miranda's illusion with TIM could speak, touch, and I bet even be smelled. I like to think of higher illusions as direct sensory manipulation, not just smoke and mirrors.
Also, the King COULD tell. As soon as the attack finished, he was instantly aware that it was way too easy. That means he was ready for the attack, and likely dodged or negated it completely.
Nothing in the comic ever mentioned the King as being a Seer.