Hmm what this is showing me is that DPS actually takes a lot more brains and initiative to play well. More than it does to play a tank or healer well. As tank and healer might have results slapped in front of them, so they can correct easily.
The DPS game is more subtle and requires keener observations and more diligent research.
This is not quite true.
(As an aside, I don't really understand why people care if DPS or healing is innately harder or easier. I care if one is unnecessarily harder.)
There are generally 3 ways that people learn to play:
1. Theorycrafting. This means looking at the math behind the game, and extrapolating tactics based on the math.
2. Trial and error. The player tries something new, sees if it works better than the old way, and decides whether to use it or not.
3. Appeal to authority. Get someone who is better to tell you what to do.
The third one inevitably chains back to the first two, so we'll discount it for now.
Of the first two, most people learn through trial and error. As they get new abilities, they try them out, and based on their experiences they use the ability or not.
A few people, though, are theorycrafters. They build mathematical models, and the models imply that certain abilities should be better than others. They test out the abilities and use the results to improve the model.
Certain activities are easier to learn or improve with different strategies. For example, crowd control is generally learned through trial and error. The difference between a good trapper and a poor one is more a matter of practice than theorycraft. Healing is very similar. Theorycraft helps, but the better healers tend to be the ones who heal a lot.
Trial and error requires feedback. Test something, see the result, incorporate the change. If you can't see the result, or if the result is hard to understand, you can't use trial and error to learn something.
So raid DPS is hard to improve if you use trial and error, like most people do. However, doing good raid DPS is relatively simple from a theorycraft point of view. Where the theorycrafters go into their long discussions and crazy math is determining the optimal raid DPS. But you don't need optimal DPS to start with, you just need good DPS.
Here's a general algorithm for doing high DPS:
1. Rank your spells from highest DPS to lowest DPS.
2. Cast the highest DPS spell.
3. If you cannot cast the highest DPS spell again (because of a cooldown), cast the next highest.
4. Repeat steps 2 and 3, going down the list as necessary.
It seems very simple, but following this will provide you with a decent spell rotation for every class. It won't be the optimum rotation, and you might have to drop a spell because it costs too much mana, or does too much threat, or has a really short range. The work comes in ranking your spells correctly. (The main trick here is that when calculating DPS for a non-burst fight, you only look at the cast-time of the spell, not the lifetime of the spell. For direct damage they're the same thing, but not for DoTs.)
This is a good starting algorithm to develop a rotation. After this, you have to consider "enablers" such as Mangle, or Improved Scorch. These are spells which have a lower DPS, but improve spells above them on the DPS chart. Then you have to see if the DPS lost while casting the enabler is made up by the gain on the rest.
And then after that, you have to consider mana costs, which is where it gets complex. But getting a decent DPS rotation is not very hard from a theorycraft point of view. (Getting the single best rotation for a given fight is where the fun lies.)
A very simple example is the Frost mage rotation. If you ranked the spells, it would probably look something like:
1. Summon Water Elemental (3 min/45s cooldown)
2. Ice Lance (against a frozen target)
5. Ice Lance (against a non-frozen target)
So when looking at the DPS rotation, you go Summon Water Elemental first. Then you can't cast Summon Water Elemental again, so you move down the chart. The boss isn't frozen, so you move down to Frostbolt. You can cast Frostbolt again and again, so you don't go further down the chart. When Summon Water Elemental comes off cool-down, you cast it again.
That's a relatively simple rotation (in the game you should also Cold Snap to reduce the cooldown on the elemental). But the basic principles apply to every class.
So that was a really long post, but it essentially boils down to: raid DPS is easier from a theorycraft point of view; healing is easier from a trial and error point of view; and tanking is a bit of a mixture of the two. The problem is that the majority of people learn using trial and error, not theorycraft.