The underlying mechanics of class 'balance' in world of warcraft revolve around the rock, paper, scissors ethic.
In that I mean, it's not a fundamental design philiosiphy for any one class in the game to be superior or even equal to all other classes.
Paper beats Rock. Rock beats Scissors. Scissors beats paper.
In World of Warcraft this means Mage beats Warrior. Warrior beats Rogue. Rogue beats Mage.
This is the core design ethic of the game and all players considered equal in gear and ability, these are the likely results of how the PVP power balance lies.
This is deliberate and a core ideology of balance in the game concerning PvP. Hence, it's pointless to argue that Warriors should be able to beat Mages.
You are not. Not according to the designers intention of the game mechanics.
So when you see a frost mage, your job as a warrior isn't to try and mash his face in because you literally cannot (unless you significantly outgear them or have a higher ability with your own class).
This is by design and intent, so don't try and fight it.