Do some math about it.
Lets use really basic numbers to make it easier.
Dual wield:
Mainhand = 1
Offhand = 0.5 * 1.25 = 0.625 (not sure here, but does not matter that much)
You lose 19% hit for dual wielding. Both weapons combined you got 1.625. Remove the missing 19% from each hand. 0.81 + 0.506 = 1.31.
Not really accurate math, but its get close.
Dual wield deals about 30% more dmg then wielding just one weapon. Not counting talents like unbridled wrath or enrage or w/e right now.
Def spec has 10% more dmg on one-handed weapons. That means you deal 110% dmg. With that dual wield is only 20% in front anymore.
Damage from fury surely is higher, but the good part about defense is that you get way less damage. Your downtimes are reduced by quite alot. Even if you can't manage to take a mob out in the same timespan you can safe this time somewhere else.
Haven't tried it yet, though I got several reports from old vanilla players who swear its the best (in their opinion) way to level a warrior.
Keep in mind you usually die if you aggro more then 1 mob on your level. With def spec you might be able to pull that off.