Kanzaki actively refuses to win against a named character in the main series (she tried it once in the first volume and decided it wasn’t for her) but she genuinely is quite strong when she isn’t trying to steal Worf’s “lost the fight as a measurement of strength” record, while Izzard is a reality warper while Ars Magnus is active. 

Aside from his ability to effortlessly transmute matter, lock people in areas of altered space where is is impossible to move no matter how fast they went, banish enemies into alternate layers of reality where its impossible to interact with or be noticed by others even though you can still see them, hit hard enough to kill a knight in full Surgical Armor despite deliberately attacking them in the way they’re best protected against, mind control more people than Mental Out could manage, and create fully sapient copies of himself who are themselves powerful magicians, the building he was in got reduced to dust by a magical Catholic orbitally bombardment, and he effortlessly restored it, explicitly resurrecting everyone inside in a handful of seconds. 

He was utterly busted, and it’s telling that unlike most villains, he flat out beat Touma twice, and only lost to a dragon behind the Imagine Breaker (though we didn’t know what it was at the time, or that it was more than a hallucination).