Most warriors, for obvious reasons, opt for the big giant 2-hander or the dual wield double agility enchant fury build because they want two things: big critical hits and lots of them.

But big critical hits don't win PvP battles. Oftentimes, just being in the battle is enough to distract important elements of the opponent's team from places they should probably be.

A warrior with a shield who knows how to use defensive stance is a royally stubborn obstacle on the pvp battlefield. They are practically immune to rogues because of disarm and shield block, and if they are in melee range, they can be a major issue for spellcasters because of shield bash. Add plate armor and a ton of health and the next thing you know you have a block of cement in the middle of a fight that is going to occupy opposing dps for some time before they can return to advancing their strategy.

Don't underestimate that shield slot. Big criticals are nice at the right time, but an intercept and hamstring at the right time can be just as decisive and possibly the key to a win.