IMO they're good for spawns, and grinding wither bombs in some situations as a pure necro.
For a general open field template I'd prefer a typical mage, w/ scribe, and lower necro/ss. The damage output can be AMAZING. Against mages the damage output is great, and you can guarantee your poison cycles if you can cycle, just gota spellblock, I suggest w/o weaken or the such incase of a leftover omen... I can't count how many dexers I kill w/ curse, Explode, Omen, Flamestrike, Omen, Painspike & something else to finish if needed lol... Especially if they have no resist, or they wasted their apple because their HP should be pretty low.
I don't find most mystics to be over powering these days. Half of them forget cycling, and think all out damage output from spellplague is enough. But they always leave too many openings for gheals
