but you dont aim in dark souls. maybe once in a blue moon with the bow you go into first person aiming
Indeed and the fun part about bow aiming is that you do that carefully, not in the blink of an eye. A controller helps with that too because it allows you to adjust really slowly without having to actually physically move anything; rather you just slightly nudge the stick and keep it in place. If you have to do that with a mouse its all depending on the sensitivity of the mouse, how steady your hand is, how clean your mouse/pad is, etc. etc. Too much room for error.
But a fast paced FPS on the other hand... I don't know how people can play that with a controller. I tried to play Borderlands 2 like that, the only thing I could do was running around drunk while missing absolutely every shot. Madness.