There is very, very few things I cant kill with spear and healing. There is a MASSIVE amount of things I CANT kill with death and lightning specifically, you can probably lump in sun, water. I agree with the sentiment to be a mage you need to spec in all trees to get around the resistances. To be melee I just need sword/spear and some armor, tactics and I can damage everything in the game. And its been a very, very long time since Ive seen a 1k+ hit from a spell. I understand you can make something viable with a mage, its just a lot tougher with less benefit.