I... just hate Grass/Dark with an admitted unnecessary passion. ;w; Dark was my favorite type before Fairy came along and seeing the Grass options for my Dark bbys physically hurts.
Okay, I admit I'm being hyperbolic.... but I'm not exaggerating that much, lol.
Obviously there are worse type combinations out there. But, to me, Grass/Dark is the epitome of "opportunity missed". It reeks of stagnancy when there's such a vast pool of awesome ideas and niches that - while obviously won't make the type less defensively vulnerable - would at least make them more badass while they get OHKO'd lol. And maybe not limiting all of them so much in movesets that they could at least be doing some decent neutral coverage would be nice. All of the current Grass/Dark Pokémon are just.. so meh. They feel so uninspired and boring and bland to me ngl. I feel guilty for saying it cause I know it's 100% subjective, but aesthetics/design do matter at least a little, so in combination with their base stats (yay mediocre attack / sp.attackers again woooo) and typing -- and I just cannot help but to believe that they've been given the short end of the stick on all fronts.
I bet Grass/Dark can be done right. In fact, I'm sure one day my current opinion to be proven wrong. But as it stands, I just find the existing Grass/Dark Pokémon to be painfully underwhelming. No offense meant to the Cacturn, Shiftry, & Zarude lovers out there! Everyone's got their own tastes and that's perfectly fine! But strictly speaking for myself? Lord, what a clusterfuck of a type combo.