I'm not entirely sure about the stereotypes about Dark, but the type in general seems to be almost as bad as the Psychic type. Dark resists only itself and Ghost, only carrying a not so useful Psychic immunity. Strong Dark moves like Crunch and Dark Pulse are often set aside for Shadow Ball, unless they are used as STAB instead of coverage since Ghost can hit ever so popular Fighting types and now Fairies neutrally. The next best attack, Sucker Punch, is at best decent unless you are running Mega Khan and Mawile or something. As a defensive type, having Dark only resisting its own, at best, 80 BP attacks is somewhat sad. Blocking Shadow Balls (the only Ghost type move in existence apparently) is nifty, but if you really want to take special attacks, just swap to a pink blob. The immunity to Psychic is not even an incredible thing to have. Sure it gives you the opportunity to switch in, but Psychics and their STABs haven't been much of a threat since Generation III. Since then it has been "Greetings, here is my Focus Miss". There are good Dark types like Tyranitar or Bisharp, but those Pokémon aren't considered good mainly because of their Dark typing.
I am pretty sure that there are terrible types that we are all aware of. For one, there's Bug. It holds a ton of weaknesses and the majority of Pokémon representing the type are laughable, but they oddly have great resistances in Fighting and Ground while holding notable super-effectiveness against Psychics and Dark types. But overall, the Bug typing is still terrible. Yes, there are Pokémon like Scizor and Volcarona that try to pull their name out of the mud, but it's not because they are Bug types. Most people consider Scizor as a Steel type since that is what carries its terrible excuse for a primary typing. Even then, Technician comes before noticing the Bug typing as a good thing. Same goes for Volcarona; epic special stats and Quiver Dance. Let's see the Bug Catchers in the next Generation of starting routes use Scyther and Larvesta.
Next, there's Grass, almost in the same boat as Bug. It supports resists to Ground and uncommonly Water. However, as an offensive type, Grass is utter ****. Although being super-effective against the afore mentioned types plus Rock is unique, Grass doesn't hit enough things neutrally to be considered a decent attacking type. Coverage or even a secondary STAB are what most Grass types need to even be seen as useful. The only thing going for Grass is variety. Status moves like Spore, Leech Seed, and Synthesis are restricted only to these types. Grass also appreciates Sun and Rain for offensive abilities, defenses against Fire, and extra Synthesis recovery. As a whole, this means that Grass needs support or needs to support in order to not be dead weight.
Lastly, Normal types. This type is versatile; consisting of speed demons, powerful physical attackers, and somewhat decent special walls with extraordinary above average health. It's just the typing itself holding these Pokémon back. Not a lot of good popular Pokémon are Normal types, unless they are extremely specialized such as Blissey or something. Six Generations of this game has passed yet no one at Nintendo has offered this type any favors, for shame. I would like to compare this type to Dragons; both barely hitting anything for super-effective damage, yet distinguishable from one another. However, Dragons resist Fire/Water/Grass/Electric which makes Dragons considered to be strong since they resist all primary starting types, but I think the reasoning behind their strength is that Dragons resist the primary elements or 'forces of nature' screw wind, Hurricane came four generations too late. Normal types should be a mirror image, finding resistances or weaknesses in physically/mentally affiliated types, Fighting/Ghost/Dark/Psychic.
If Game Freak ever tries to edit the type chart again, and hopefully they do, a few changes in favor of the above types would make the game somewhat enjoyable for those who chose the hard path in the past. You know, the people who think Dragons, Steels, and other popular types are too dangerously close to being considered as mandatory to have on all teams. I think a majority of the suggestions would make sense, but this is mostly for evening out the battle field a bit (Flying Resists Fighting and Ghosts Beat each other so dump any logical comebacks).
*Poison Resisting Ice, Bug Resisting Water, Grass Resisting Fairy/Fighting, Electric Resisting Bug, Ice Resisting Water/Dark/Dragon, Normal Resisting Fairy, Fire Resisting Flying, Dragon Resisting Flying, Psychic Resisting Fire
*Poison Beating Dragon, Steel Beating Dragon, Normal Beating Fairy, Dark Beating Normal, Ghost Beating Ground
*Grass Neutral to Poison, Psychic Neutral to Steel
^ TLDR version: We will never see anyone using these types for the sake of these types and by anyone I mean Ace Trainers, Champions, competent Players, ect...
