It works as a starter triangle. The only thing a starter triangle needs is for your rival to have an advantage over you. And no, the advantage Dark has over Psychic is not unfair. Shut up.
I agree that it Dark > Psychic is fair on the starter triangle. Since when do you go for the non-SE move in the first place? And for that matter, they never even start with their STAB moves anyways, and by the time you have them, you have other moves and other pokemon you can use.
I'm pretty much fine with Grass/Fire/Water. I just wish that either Fire was more common, or Grass and Water were less common, because I always feel like it's a waste when I don't pick the Fire starter.