(I consider this idea to be secondary to Classic Maplestory and actually this one would have the most effect in a Classic setting)

When the Edelstein Resistance jobs first released, most everyone thought that they were over powered. What if the 5th job advancement led to joining the Resistance and gaining the strongest skills from each of those branches? Then their original OP'dness might fit a bit better. Although there would need to be a Thief job added and for the region to be more dangerous.