Honestly, I think those Mortificators are absurdly good for their 20 points each. They are pure killers, extreme hard to kill with their Dodge and to make matters worse they can enhance their armour with a spell as well. I positively hate that troop type!
Regarding the mistake… you are right, this was against the rules. That being said, we made a couple of mistakes that benefitted the Brotherhood as well. Like for example the two Mortifacators that fumbled their grenade throw. Had we played that right, they might have been killed by their grenades going off in their hands. Since those two eventually killed my Warlord, this could have been a gamechanger. So I guess bottom line is, that it all probably equalled out!