I find this really weird ... I have totally stopped using Curse of Doom in that fight as it gets wiped each and every time. I find it weird to see it used and it works, on this here. For me, the Unborn Val'kyr is almost worthless if I try to use the Curse of Doom, since, in my case, it was wiped 3 times, more than once, meaning that the Gladiators know you just put up a big gun, and they know when to wipe it. Thus, I began relying on the other spell (small heal with it) and then use the other spell on the opposite side of UA. After that, I allow the Creepy Crate to make sure it can do damage twice to the other pets, so they have less Hit Points, which is the biggest and most important part of the fight ... and the rest is easy.
These gladiators, losing 450 to 550 points each from the Creepy Crate is the biggest advantage there is. Again, I have found CoD worthless and a waste of time in this fight. I think we need to remind ourselves that there are several/many alternatives that we are not used to using, and in fact, have no idea how to use. You kinda learn this quickly if you ever tried taking Fungal this or that or Withers, all the way up to 25 ... Very slow, and trying ... but a bit on the side that we are not learning on many of these fights?
I'm actually thinking of trying to get 2 Creepy Crates, just for that fight!
Another example, is using Chrominius against Veeshar in the Spires of Arak, and using Howl and the Bomb. Actually not very smart at all, when you can use Arcane Explosion exclusively, and when you get done, the first pet is down to 200 points (or so), another pet in the background is down to 200 points (or so), and the 2nd pet is in serious bad shape. You bring in the Mechanical Pandaren Dragonling, pump Moonfire (AoE damage), and the 3rd pet dies in the background, and you only have to deal with one pet that revives with a few hit points, and the fight is over. Using the Howl and Bomb here, is a waste, when you could easily help yourself by making sure the other pets have less to work with.
THIS, btw, is a strong strategy on many of the fights in the jungle ... you take AoE damage, and your pets are taking it hard, and making the fights sometimes more difficult than they need to be, and it is advisable, to take into consideration that ability to use AoE's and when, and also learn how to defend them ... because they are big problems otherwise, if you think you can just bomb once and its over.