How bizarre. This is the last page but it's not the hoh_latest page.

So what Theo is saying is that mages lost due to overconfidence, known as a slow and insidious killer.

sounds like Black Crystals are not a be all end all for stopping magic. a mage just has to learn how to counter the effect or build a resistance

Damn...
Imagine World where population actually is managing to pull off a semi succesfull magic purge despite Magic users being truly as dangerous as can be imagined.
Mostly because adult magic users that believe in their own invincibility are honestly weak even to sucker punch with regular weapons when caught off-guard. And weak to goldplated weapons even when they are on guard.
And THEN it's all over because one country manages to mass-produce a perfect anti-magic weapon. But instead of sharing it they decide to monopolise it in effort to become a Empire.
Which not only made a whole bunch of other countries STOP their own Purge as they found themselves in need of strong fighters to counter Kragmoria. And wasting lives of regular soldiers in fighting magic users become less important.
But Magic Users themselves, finally aware that potent anti-magic weapon exists finally got over themselves and started doing stuff to adress certain things.

I think based off what see, black crystal shuts down the ability to use magic of whoever touches it and grants magic immunity similar to what like Burke has.

So a person holding black crystal won't get hurt by attacks of pure magic but if there's an actual physical component it will still injure them. Also if a magic user is physically fit and trained in combat they can still beat an opponent without magic.

Theo could do some type of flash step that let him drive a mundane weapon into a black crystal holder and rapidly withdraw. And he still had the level of physical strength even when the crystal was touching him to taken down enemies.

I'm guessing most magic users ignore the physical training aspect and are pretty over confident and uncreative in their abilities. So Theo used the Black Crystal to help train them by shutting down their magic (both showing attacks having no effect and sealing their magic) to help motivate them into training more.