What do you mean by mass suicide? If you mean "throw one hero at them to weaken them, let him die, and then attack again" that doesn't seem to work. I've tried that before, and the very next turn the province seems to have all its defenders again. (This is for neutrals. Against the AI it works just fine.) Weird... all the medusa in my encounter had 6 or 7 ranged defense. (Outside of swamps. In swamps, it was 1 higher than that.) Using units with high resists is a good idea, though. I'll give that a whirl.