While this can happen, it doesn’t always happen with every weapon. I also noticed that on easy, in the mission where you discover that you can just run under the shields of the enemies, the bomber strikes can 1-hit KO you. I’m assuming that the stuff that the infinite armor doesn’t protect from is scripted destruction/death. Driving a tank into water will also make the tank explode. The best strategy is to simply be aware of what weapons will and won’t do this and avoid the ones that will. I’ve stood right in the satellite strike laser beam, shot ants at point blank with the sniper limpet and some other stuff, taking no damage at all on the highest difficulty. It seems to be stuff that has large blast radius that will insta-KO you, but not all of that will always do so. It’s just they have a higher chance of doing so. With infinite armor, no reloads, and rapid fire, even the level 0 and level 1 or 2 stuff is viable to use to farm more gear.