there is only 1 talent that grants temporary relief to damage, does that mean you're designing this with Dark Bargain in mind ?
Also removing the unkillable from that ability yet retaining it's overall mechanics ( channeling for a few ) and retaining it's normal cd while simply reducing it's channel time to 3 secs doesn't exactly fix it , I'm still trying to decide what you want us to use this spell for exactly.
Since it's no longer an Oh shit button that means we've moved towards the actual CC/ window opener meaning that we want to use this spell to peel or to create windows in order to cast, we've been focusing a lot on whether melee can be hit by this since they can walk out of it ( since I assume they only get stunned in they're inside the blast radius which significantly reduces it's effectiveness), we've yet to talk about how we use this vs ranged classes , you want us to run up to a ranged class in order to try using this on them ? most of the time they can kite around or stop you from doing so, and more importantly, sometimes moving into the open might place me in a very bad position which could turn into a extremely bad disadvantage for my team.
It is significantly easier for ranged classes to avoid this ability than melee, if we're having problems with landing this on melee we're surely not going to be landing this on ranged classes, the only timing where this could fit the bill is when we're in a position where the teams are stacked or caught off position, in which case good players avoid these situations with all their will so the amount of usage this ability gets the higher we climb the ladder is significantly reduced.