No, Warriors are not "that bad" at PVP, infact they are the best pvpers if played right. They have the ability to take on any class at any given time, while some classes might be more hard (mages/priests) they are still able to be killed if you can close the gap and get a hamstring in. Here is what you should do against any given class:
Druid:Rush and hammstring, wait till they are at 25% health and pummel their healing spell. Dead.
Hunter: Hammstring pet, if AOC is put on pull out ranged wep and shoot, then close gap and hammstring the hunter, continue this untill you close the gap. Keep pet hammstringed. Close the gap and you win.
Mage: Pummel arcane tree, and hammstring. If mage gets the jump the hardest part is gettin in range to attack, wheh you get in range you win.
Pally: Enough said.
Priest: Pummel holy tree annd hammstring. DO NO PUMMEL SHADOW TREE. They key is to0 get hammstring on before they fear you or be an undead warrior
Rouge: Keep gouge on them so they cant vanish and then hammstring them and then they are done.
Shamman: Kill their totems and hammstring them. Pummel their healing move and you win. ( Not that sure on shammy, this works for me in duels, I dont pvp them since im undead)
Warlock: Very hard if not undead. Use inner rage, and intimidating shout. And pummel any move you would like to. ( not to sure since Im undead and i cant be feared)
Warrior: Comes down to who can play the class better.
Feel free to comment and please add on to Shammy and arlock guides.