Sigma in this mode is SUPER useful. Because of the damage increase, his ult is able to one shot all the omnics, including the Orisas. For supports, I highly recommend Baptiste. He can easily heal multiple people at once with his healing grenades and regen burst, although Moira is also fairly good at this. His immortality field can protect you for a few seconds to help take down a bastion or revive a teammate. His ultimate can make quick work of anything, but mainly should be used for things like detonators, bastions, and orisas. Orisa is also recommended for this just to have a second barrier to work with, but she could probably be replaced by another tank. Ideally the fourth slot would be someone like torb or bastion, but we had a genji here and we were able to beat it.