Time ago shaiya community had a long and deep discussion about caster problems and how to fix this class.
After a long brainstorming Aeria staff agreed with the community that a change was needed and the fix that was identified was that the magic resistance should cancel 1 magic damage point and not 2 how it happens now.
Anyway apparently the developers didn't like this change cause it has too much impact on ingame mechanisms and this fix was delayed, at a point that now it seems it is forgotten.
Now EP6 came and with it a new skill that will grant to the whole raid 50% more magic resistance: this, together with the fact that ep6 gear and weapon give to casters the lowest attack and defense in regards to other classes, killed the caster class (N.B. I didn't say "may kill" or "will kill", I said killed. No one wants to play anymore this class and almost no one plays it anymore).
The only reason there is not much complain on forum about it - while there are lots of complain about the +50% defense skill of defender/guardian - is because no one plays anymore casters, so no one cares about this class issue.
Now I want to propose just a little change that will really change everything without much effort on developer part.
Change the +50% magic resistance buff to a +50% magic attack buff.