Who Should I Add To My Team (or should i keep it the way it is) Pok�mon Platinum?

Drifblim's a great wall. You should keep him in. Just from experience, here's my favorite strategy. Get a Gallade and a super wall with follow me. Make the wall tank the attacks while Gallade swords dances up to max attack, then continue with agility. Once you have full attack and good speed, take out the enemy's team with Psycho Cut and Poison Jab.