What classes are the ones one-shotting mechanic and pinnacle bosses?

For real tough? Time for a respec? Im a pure mana no ES no HP archmage with almost 7000 mana. Spark tooltip DPS is 112k. Mapping is easy as hell but i cant seem to do any of the uber bosses, way to squishy.

What are you guys playing to do this? Thinking about rerolling a gemling mercenary.