Don't take people at face value when they say that Survival is more damage than Marksmanship. Maybe overall for the raid while Expose Weakness is up, but not for personal damage by a longshot.
Compare a 7/41/13 build to a 0/21/40.
For damage, Marks has:
Imp Hawk
Focus Fire
Barrage
Ranged Weapon Spec
Trueshot Aura
Careful Aim
Master Marksman
Surv has:
Surefooted
Survival Instincts
Killer Instinct
Lightning Reflexes
Expose Weakness
Suppose the hunter has 533 agi, which gives them +80 from Lightning Reflexes.
Between KI and LR, they have an extra 5% crit. With Mortal Shots, this works out to being about +5% total damage, so scratch Ranged Weapon Spec.
The extra 80 AP, and the 1/4 of 613 = 159 AP from Expose Weakness total 239...assuming EW is even up all the time. Trueshot is 125. Master Marksman's 10% - Survival Instinct's 4% leaves a net of 6% AP for marks, which is still probably enough to make up the difference. (It would take 1900 AP if EW is constantly up, so *maybe* not.)
And that leaves Surefooted...which might not even be useful considering how much hit rating we have on our gear right now. By contrast, marks still has +2% damage, intermittent 15% haste buffs, and extra damage on Multi Shot.
Now, notice that most of the remaining effect that the marks pulled ahead with was from their Beast Mastery points -- points the survival hunter could very well pick up as well, but would cost him Mortal Shots in the process, which makes this a very different argument. Sure, you COULD spec 7/21/33, and some hunters have done this, but then you're missing out on some of the other key end talents in survival...namely Thrill of the Hunt.
Where the beauty of survival lies is that they need to care about less stuff on their gear. Sure, they want agility more than anything else, but they also don't need hit gear because of Surefooted, they don't need as much mana regen because of TotH, and arguably they need less stamina because of Survivalist and Survival Instincts. As a result, the survival hunter can place a greater focus on Agi, AP and crit.
But generally speaking, marks will still do better damage than surv. It would take a hell of a lot of agility to compensate for that.
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Only the exceptions can be exceptional.