I'm sure everyone's already said it, but why not use something like psychic->fighting->dark instead of electric->normal->dark? Then psychics wouldn't have to be labeled dark; you could use psychic for all the poison types, just like in the card game, The fighting types wouldn't have to be electric. And people would not have to relearn type effectiveness
Not the dev, but they probably did it this way for simplicity, instead of coding 18 different types, they made 6 groups of three so its easier to balance. Don't get hung up on the original games types chart, the only onde you need to learn, and that takes 2 minutes, is WHITE > BLACK > YELLOW > WHITE.
Just as a fun fact, here's all the original types inside every Pokémon Overlord type:
White: Normal, Flying and Fairy
Black: Dark, Psychic and Ghost
Yellow: Electric, Fighting and Steel
Red: Fire, Ground and Rock
Blue: Water, Ice and Dragon
Green: Grass, Bug and Poison