Another point to consider is how armor interacts with resistance. A good example is the cyberdisc vs. AP damage. They have only a 20% resistance to it, yet they are effectively immune because their strong 40 points of armor is not easily penetrated by such low damage values as AP weapons have in the vanilla game. The 56 damage of a heavy cannon AP round is reduced to 44.8, barely higher than the armor, meaning there's only slightly more than a 50% chance of even dealing any damage at all. In this case, the 20% resistance actually makes a pretty significant difference. With no resistance, the heavy cannon AP is almost as powerful as a laser rifle. But the laser rifle is still much better because it is more accurate and has a much higher rate of fire.