I just did this on my warlock. Took a few wipes and attempts at using the advice that I read here. I finally got it, but I did not use my GoSac as some mentioned had worked for them. that didn't work for me. Instead I used my voidwalker as a tank the whole time.
I also had trouble dumping aggro with my soulshatter, but maybe I used it at the wrong time. (I still used it just in case, tho, as the fire blobs came at me).
I am destruction. I got a bunch of people to buff me up when I was at the shrine. I placed a demonic circle up on the balcony and then I went up to the balcony and placed my gateway going across from one end of the balcony to the other, parallel to the stairs, tho placement may not matter so long as you have it up there to use to dodge everything.
When the fight first started, I immediately sent the voidwalker out to start fighting. He held aggro while I stayed outside of Wrath's range. He held aggro on the fire blobs that came out, too, for a while. If you are lucky that Wrath's back is to you or if you can get behind him, you will do extra damage. The blobs finally started coming at me, so I ran up the stairs (didn't even use my demonic circle) and used soulshatter. I was able to run around and kill the fire blobs while my void was still fighting down below. I had to use the gate a lot to get away, healthstones, fear, drain life. I could then stand on the stairs and blast Wrath for a while until the next round of fire blobs came at me. My voidwaker came up to help me. We stayed up there, fighting the fire blobs as they came around. I guess the mirror image stage was going on, I could not see what was happening below me-- only saw some dust clouds.
The fire blobs die pretty quickly, but you have to keep moving (which sucks now that we can't cast as many spells while moving) because they will come at you quickly and will do a lot of damage. My void would get aggro on them enough for me to drain their health or only have to worry about one at a time. A couple bigger ones will spawn up there on the balcony, but they arrive one at a time, so nuke them as they spawn.
I had to use Flames of Xoroth to revive my voidwalker at one point, and I had to heal him a couple of times. Wrath will stay below the balcony for most of the fight, so it is a lot of dodging and killing fire blobs.
Wrath will finally come upstairs. My void was holding aggro on him, and I was able to stay out of range of his spells while hitting him with what I could. A fire blob would come at me, but i would run, fear it, kill it, go back to Wrath, and repeat. I could goblin hop or use the gateway to get out of his range. I summoned my infernal toward the end to help out just in case, but my voidwalker was keeping Wrath busy. At the end there, I had to run down the stairs a bit to kill 2 fire blobs that were on me before I could go back up and finish off Wrath. Backing a little down the stairs to kill the fire blobs got me out of the range of whatever Wrath was blasting, though.
It is true that you have to be patient and take your time and keep moving around. Bring some heal potions, bandages, whatever will give you an extra boost when you can, and drain life from the blobs that are far from you or from Wrath when he is far enough that you can reach him but he can't reach you. You will have to switch your focus from Wrath to the fire blobs... when I decided to finally take them on and kill them when they came at me, I was able to do it. At first I was just trying to run from them or fear or drop aggro or aoe while I kept my target on Wrath, but I was too busy with that and couldn't get big hits off on Wrath and they would catch up to me and kill me quickly. So just deal with them while your voidwalker is either helping you or keeping Wrath busy down below.