I've only tried Chimpeon with a Hunter and melee classes so I can't comment on or confirm the "poor DPS" for casters. However, if you have an optimal TellMeWhen rotation profile and Chimpeon is setup correctly then it would be difficult to beat Chimpeon's DPS compared to doing the rotation manually. Unless of course you have the reflex of a Star Nosed Mole (they're fast)!
The Star-Nosed Mole
Try a TellMeWhen class rotation available here and see if that improves your DPS...
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