It isn’t.
Reading your comment makes me want to see a Nullification-based Battlemage set (with some Soldier damage source, for once not necessarily Cadence) with Nulli applying nonstacking RR and having 5-6 seconds off its cooldown. Think that’d be a neat concept/playstyle.
Fumble on Terrify is a great idea too.
Edit RE: Zantai
My sabo post was not suggesting for new items to be introduced, if that wasn’t clear. This post is, though. 
Edit 2: I was so infatuated with the idea above that I decided to throw it together in a mod. Check it out here.