I've crunched the numbers, and my primary question - how have DPS DKs scaled in relation to other classes - has been resoundingly answered. In addition, loads of additional findings and questions have been raised by my trip into Dataland.
I took the top ten dps of each class/spec for each boss fight on normal ICC25. I obtained an average dps for each spec on each fight. You can easily examine each boss to see which fights are 'melee-friendly,' 'ranged friendly,' and which classes do well on specific fights. While certain strange events occur and can skew the data, like Dusk's crazy speed kill of Lady Deathwhisper, there is enough data here to smooth out any bumps. Regarding the above, two marksmen hunters for the LDW fight did very well - doing more than 5k better than any other hunters. This made hunters look better overall, but averaged across all 120 data points (10 hunters for each of the 12 fights), hunters still were found to be about the 5th best dps class overall.
In the end, I hand-entered 4,200 points of data, giving a very good sample size from which to draw conclusions about how each class/spec is scaling as guilds continue to progress and gear up in ICC.
Remember, I chose the top ten dps because I'm interested in what the maximum dps potential is - so even if it's not realistic for every class to get power infusion, or tricks/hysteria all the time, or to have the luxury of staying on the boss the whole time, we're looking at what CAN be done under the right circumstances.
Destruction warlocks, survival hunters, and blood DKs did so poorly on examination of normal modes, that I saved myself the effort and didn't calculate their scores in heroic modes.
I just noticed my Sindragosa data for heroic got pasted over the Lich King info. I'll check this and repost if anything changes. As far as DKs go, though, this will only hurt. Their best fight in ICC relatively speaking was Sindragosa.
1. DKs are in a sorry state. Unfortunately, my hunch was borne out, conclusively. On examination of Normal modes, DKs started in the middle of the pack through Festergut's tank n spank, and faded fast to the end. By the end of the 12 fights, the BEST DK spec, unholy, was beaten out by at least one spec from EVERY class except poor, poor shammies. Unholy came in as the 11th-best dps spec in the game, and frost was 14th. The by-now-abandoned blood spec came in dead last - 19th - of the specs I looked at.
By the way, I did eyeball beast mastery, arms, and subtlety, but as expected they were so poor I didn't even put in the effort to add them to the chart. (well, arms did ok on some fights, but fury is so vastly superior that it wasn't worth it).
In any case, the expansion-long public perception that Death Knight are overpwered can be conclusively rejected at this point. THEY ARE THE SECOND-WORST (OR THIRD, MAYBE) DPS CLASS IN THE GAME right now.
Heroic modes wasn't much better. All of the 'Shadowmourne classes' (Warriors, Pallies, DKs) did see some improvement in heroic modes, but DKs once again scaled the poorest, by far. In fact, they still ended up the third-worst dps class in the game, barely passing priests, despite the fact that if you don't have a Shadowmourne, you can't even get on these charts. I didn't look at every fight, but on every one I did look at (Saurfang, Festergut, Sindragosa), EVERY Warrior, Paladin, and DK on the charts had the legendary. Do you scale an entire class around the assumption that they have the (very rare) weapon? Even so, DKs come out smelling putrescent.
2. The rich get richer. It's been well-known from vanilla and through two expansions that warriors scale well with gear. The proof is here. Blizzard has stated their goal for all dps classes to be as close as possible - within about 1-2% of each other, with the 'pure dps classes' on top.
The 'pures' didn't do too badly with the four classes filling the 2nd through 5th spots on the class charts, with the exception of warriors. Warriors finished 2% better than the second-best class (spanning the stated goal for all classes from their nearest competitor) and more than 17% better than the poor enhancement shammies. On heroic modes, they got even richer, finishing a full 6% better than second-best, and over 25% better than enhance shammies. As a hybrid class, that's hardly in line with Blizz' goals, and hardly fair to other classes. I'm not QQing here - just presenting the information. I like warriors, but clearly their dps is out of line with 'balance' in the game.
In heroic modes, Retribution used their Shadowmournes to leapfrog several 'pure' classes to finish in the third spot. Unholy did benefit from the legendary, but just not nearly as much as the other two classes.
And as has already been stated, the dps for shammies was much worse than any other class. Obviously, Blizz' announcement that there will be other heroism classes paves the way for shaman to get a big boost - and rightfully so.
3. Other observations: (some of this I'm sure many of you knew already; I'm no expert on every class):
-I was surprised fire mages did so much better than arcane, particularly in better gear. They were convincingly the second best spec in the game. Arcane did quite poorly in heroic modes, dropping six spots.
-Overall, the melee vs ranged divide was well-balanced. There was a fairly consistent split between ranged and melee overall, and there are several fights in ICC which favored one or the other. Decent balance.
-Rogues can't complain too much overall. I've seen lots of concerns with how they've scaled. Obviously, combat is doing fine, so one can't complain too much. Of course, if one is referring to mutilate, then yes, rogues have a point, but at least they have ONE spec that is doing well.
-Balance isn't scaling well. Balance druids did fairly well in normal modes, but hardly saw any increase in dps in heroic modes, and saw their relative position on the charts drop significantly.
-Shadow priests aren't as bad as their reputation. But, they could do better. They still ended up as the second or third worst class/spec, down there with DKs on the junk pile.
-Demonology warlocks aren't doing too badly. Yes, affliction is the 'best' spec in most cases, but Demo is actually viable, and proved itself to be better than destro. Destruction - once the 'only' spec for raiding locks, has fallen on hard times.
-Blizzard needs to allow pets to benefit from buffs. Fights like Blood Queen Lana'thel really hurt when your pet doesn't get any help from the buff you get.
I'm not going to try to cover nearly everything here.
In fact, I'm only going to talk briefly about DK scaling, so for additional discussion, please leave a comment, or link this post in a forum somewhere :)
Why are DKs scaling so poorly?
1. Pets scale poorly. As a pet class, we may benefit from increased crit or other buffs, but the pets don't.
2. Knee-jerk nerfs. I've written about this previously. Early in beta and to some extent in Tier 7 content, DKs were certifiably overpowered. Since then, throughout the expansion there has been a perception that DKs are too strong, and that doing good dps is 'facerolling.' More recently, two abilities that needed adjusting - Tier 9 set bonus, and Scourge Strike - gave the impression again of being overpowered, but were nerfed to the point that the class has fallen behind. Frost DW was nerfed during Tier 8 content and still hasn't recovered even with some 3.3 buffs.
3. Other melee classes get more benefit from gear. Because DKs are a hybrid melee and spell based class, improvements in gear do less for them than the other melee classes. There are several ways to potentially fix this, from buffing talents that increase spell damage more from attack power, to adjusting the percentage of physical damage on abilities like Scourge Strike even more. Increasing the coefficient on obliterate etc is also an option.
4. In any case, Blizzard has made a commitment to continue balancing the classes. I hope they're monitoring the data that's readily available, and can give a little help to the poor classes (which right now are shaman, DK, spriest, and balance druids) and bring warriors back in line with other hybrids. I know they're focused on Cataclysm at this point, but there's lots of time to improve the raiding experience in this expansion still, and I hope they don't abandon us to our plight.
Enjoy the data, all you nerds out there! :)