I have had enough of the stun gun, stun cuff ..... crunch

I agree that this was designed to make sales (just like everything else), and there are reasons beyond that, the gear that is most used is because its most useful. Take mk5 stun gun for example + 600 health +40 str and + 2% tenacity. These are notable gains at g9, the str bonus alone is almost half the difference in str between a 6* and 7* provided the str multiplayer is +1.