Do we have a range number for this "spell"? Or a "cooldown" timer? It "feels" like 20 yards and 5 seconds but that's anecdotal at best. It does however appear that there are times when the animation occurs and yet I escape and I'm wondering if range or glitch or mistaking the animation for something else entirely (this seems the least likely).
I'm hoping that perhaps someone has attempted to quantify this already.
I am not sure of range and cooldown, but most of the times that you "escape" are caused by movement-blocking objects along the vortex path. If you are within range but could not walk in a straight line from your current location to the monster, you will be picked up (losing control for a fraction of a second) but will be stopped at the obstacle (similar to Demon Hunter's Vault). For this reason, good use of terrain can make it easier for kiters to deal with vortex, as there are a lot of objects which can't be moved through yet allow projectiles to pass. It's the smaller of these objects that give the illusion of an "escape."