Magic swords shatter the instant they come into contact with his right hand.
He was shot in a recent volume....and immediately escaped the ICU to save some stranger in the epilogue.
Outfighting him is one of the few ways to truly, decisively beat him, and he actually does get beaten so badly that he's half dead and concussed but he still ends up getting up and wobbling into battle, despite barely being able to walk.
The problem isn't beating him. The problem is getting him to stay down. Yes, you could make the argument that shooting him in the head would solve everything, but that's easily explained by the traditional fictional magician mentality: most magicians would rather die than use non-magic methods of combat. Only a select few heretics would consider that option. One magician actually does try to shoot him, and according to her, the act of doing so was essentially the same as "throwing away her pride".