Expertise doesn't give you a bonus damage on other people with the same amount of expertise. If you have 1200 and they have 1200 it is the same as you both having 0.
This is why people hate 50 when they start if you have 1000 expertise and they have 1350 you are fighting someone as if you have 0 and they have 350.
<50 PvP is more fun for a lot of people because it is not even close to as competitive, you can do well without any real PvP skill or gear and you end up fighting level 14's with almost no talents.
The amount of damage reduced by expertise is less than the damage increase of the same number.