Another problem is that you are seeing it from the game design perspective. That tank clearly showing where to fire? It's done to give the player a counter action to that and create gameplay. And when you are playing a game is different to being in actual battle, it may seem easy to dodge that sniper bullet, but if there are objects blowing up around you, gunfire and other visual/audio noise you may never even see that sniper. One last point is that even with the Hive seeming mindless they still have intelligence to use weapons, ships, and various other technology. Only the thralls are really the mindless ones.