[Daisuke]

How about nerfing their spell's will scaling and buffing Charge Mind? This way their damage is about the same and more about their nuke pattern instead of going "CM, nuke, normal spells till you die". It gives whoever you're fighting a window where Evokers are weak and being able to deal with CM becomes a significant counter.
Basically, tie most of their power into CM to make them more about being nuke mages instead of really strong mages with a strong buff now and then.

I dunno if it's necessary but I do think if you were going to change Evokers, that would be a good place to start.