Normally, I would feal like a hypocrite of sorts if I were to rate a team, seeing how I took a long break from the game and only been back at it for like a month now. However, I see alot of weeknesses in your team, as Wii4Mii pointed out.
However, it isn't just what pokemon are able to KO most of your team, but the fact that your Pokes don't support eachother that well. For example, hippowdon's sandstream can be a hindrance to dusknoir and roserade. And should those be the only one's left on your team and your opponent still has a tyranitar, then sandstream can aid your opponent easy.
One thing you need to work on is team dynamic. Have one poke in to support the other as well as hold it's own. I personally love abilities like sandstream and drizzle, but I won't have em in if they could be a hindrance.
Also, in my opinion, it is best to use EV's as early as possible. Plan out how you'll raise your pokes from the beginning. Otherwise, you'll find some of your pokemon will have odd stats that don't suit it.
This is completely off topic, but yes, Gravity has an accuracy/evasion modifier.