Ranged mobs are stupid. They run away when you come at them and if you run away instead, they follow you. So what you do is, pick a spot you want to lure them in, run away and start casting tornados there. Once they reach that spot, stop for a little bit and keep casting tornados. The good thing is, if you run away from them, they will all bunch up while chasing you. Once you think you have enough tornados, teleport in and immediately start casting frost novas and etc. If you have enough tornados and cc, your frost nova should freeze them until they die. If they somehow manage to get away, rinse and repeat.
Now, this strategy obviously won't work against certain affixes consistently, such as teleporter and shielding. Fire chains and arcane enchanted are also a pain but at least this strategy should make these long fights a little shorter. I might make a video of it if people are still having trouble but for now, take care and have fun!