Regarding Grand empress heroic mode, I've been searching for videos on youtube that does NOT involve a disc priest since we don't have a priest in our 10 man raiding rooster. If any one can find a video that does not involve a Disc priest in their set up, could you post it here please?
We did a kill (25man) without a disc priest, basically make sure everyone is standing in a healing rain so they maintain the extra health buff.
That alone + good CD management should be enough.
Also, definitely use 4 healers. DPS check is easy to meet.
Yes, just use your Healing CDs properly. Healing Tide, Revival and Tranq are all strong for corrupted dissonance. Don't be afraid to use 2 for each corrupted field. For example one a few seconds before the explosion and another right as for example.
Atfer 10% raid damage nerf in P1 your comp should work easily. Like said above make sure everyone is in healing rain constantly and use raid cds for corrupted field + explosion. Have people use personal cds + whatever you have left for raid wide cd for the 2nd one and you should be fine. CD management and people being smart to not run into eachother to cause aditional unnecessary splash damage. If you have paladin in the raid let him spec into double bop so he can pop it on the person with cry of terror debuff standing in the field few sec before it explodes. If you lack bops make sure you use some strong external cd for that person.