Ignoring defence

It would be because magicians use magical attacks with element atributes.
Reseting that atribute bypasses that resistance.
Am I right?

Not if it's elemental attacks against physical resist...?

I believe that some magician skills are flagged as physical element.
Magic claw is one off the top of my head, as well as some Evan skills.
Reset would make those skills immune to resist.

Ah, I see. So the archmages would not really have many such skills in their attack repertoire anyway, I don't think.