So one of the things to consider is that the Darkness subclass have a variety of aspects to alter your play style rather then multiple choices of melee. I honestly find Strand is the most versatile and flexible subclass with the number of amazing and interesting aspects that can alter our core playstyle more dramatically. We also have a number of melee abilities that barely ever see play. When was the last time you saw an experienced Arc Titan use Balistic Slam? Or a Solar Titan using Hammer strike in PVE? How about a Solar Hunter using Lightweight Knife? Some times it is better to have less build craft bloat. Once they choose to add these abilities they make a commitment to having every one of them be woth while in one situation or another while not being consistently over shadowed by other choices and combinations. The more options we have the more potential build variance. More build combi potential means more combos to try and balance against one another. The more they need to focus on balancing the less they spend focusing on creating new content. It is important to keep in mind the consequences of what your asking for and the ripple effect of each change or additional bungie makes to this game.