I believe their answer to this topic on an interview was "don't you think being in a relationship with a gun for ten years would get boring." Its bullshit. Btw, there was 1 weapon that really was overpowered when it first appeared: the vex mythoclast. People would leave crucible matches if they saw someone using it on the other team. Then bungie nerfed the shit out of it and it became almost useless.