What changes after AQ40 that makes their dps more viable?
http://www.wowhead.com/item=22194/black-grasp-of-the-destroyer
Classic Stats:
Black Grasp of the Destroyer
Equip: +28 Attack Power.
Equip: Improves your chance to get a critical strike by 1%.
Equip: On successful melee or ranged attack gain 8 mana and if possible drain 8 mana from the target.
Hunters weren't especially bad or especially good before this item. After getting this item and then picking up the right pieces of gear, their DPS is within the "acceptable" range.
Note: Using FD+Drink is quite frankly, almost never acceptable.
On Aimed Shot & Multi-Shot.
Patch 1.10.0 (28-Mar-2006): This ability now has its attack power normalized the same as melee instant attacks. This means that the attack power contribution from all ranged weapons will be the same, no matter what their speed. All weapons will contribute attack power as if they were 2.8 speed. Weapons slower than 2.8 speed will do slightly less damage than previously; weapons faster than 2.8 speed will do slightly more damage.
Patch 1.10.0 (28-Mar-2006): Multi-Shot - This ability now has its attack power normalized the same as melee instant attacks. This means that the attack power contribution from all ranged weapons will be the same, no matter what their speed. All weapons will contribute attack power as if they were 2.8 speed. Weapons slower than 2.8 speed will do slightly less damage than previously; weapons faster than 2.8 speed will do slightly more damage.
This means using Aimed Shot and Multi Shot with a fast weapon will deal similar damage to a slow weapon. It's not exactly the same thing, there are some differences which I won't go into.
However, this approximately means using a faster ranged weapon should produce more damage, both because you have more mana from BGD and therefore use more shots or higher ranked shots, and because you proc Improved Aspect of the Hawk more often, which means your DPS is noticeably increased by the Haste it grants.
Until you pickup BGD, slower weapons may yield higher DPS. But you won't have the mana to use AS and MS every 10 seconds until you pick up a decent bit of gear that supports the rotation.
And of course, it's all dependent upon if you can keep your pet alive or not.
Edit: And on DS8, it's true that it provides a very good amount of DPS for a very long time, that having at least 2 Hunters with the full equipped set is a very good DPS increase that would last until some combination of BGD+T3 is opened with specific weapon choices to boot. So, yeah DS8 is definitely "the" armor set for an extremely long period of time, for at least half of your raid's Hunters.