Yup, Glitter's right, forgot about those 3 types.
Gyroh I'm guessing your not super familiar with today's metagame standards, which is totally fine. Sadly some of those dark pokes arn't quite making the list, mainly Houndoom, It's not bulky/fast enough to pull off Sunny Day.
Dragonite's usage only really went down because Salamence and Kingdra gained Outrage in Platinum, before that it wasn't uncommon to see them from time to time.
Actually, I'm not familiar with any metagame since I've never battled competively. I own Ruby, haven't played the new ones yet. So, all I know is not based on experience, its based on reading. I looked on GameFAQs for movesets and thats where I found out about EVs, vitamins, natures, movesets, and everything. I raise Pokémon to lvl 100 with proper EVs and movesets, though the only place I can test them on battle is on the battle tower since I don't know people that still play these games.
But still, I mean, they may not be the best Pokémons to use, there are better, such as the OU, but that doesn't take the fact that they are still good and can actually do something in battles. They are not completely useless. I'd rather use uncommon Pokémon than OUs because it kinda gets old to see the same Pokémons in battles IMO. Unfortunately, my chances of winning are lowered.
I'm still thinking Dark types are fine, there are other types with worse Pokémon, such as Bug type. How many of the bugs are actually useful?