Her ability to strike at weak targets at the back of a formation is invaluable. Putting someone's Shayd or Smoulder or Adamanti out of commission for a round or two can make all the difference between winning or losing.

Rhize is a valid replacement for Cianna but lacks the stunning utility she has. Still, with the potential to do double or triple her skill damage, he's certainly worth considering. Some also replace Cianna with Adamanti or Smoulder for the same reason.