Blood didn't just need QoL changes. DK tanks were fine in T11 for most single-target boss encounters. They only really fell behind in T12H when paladins and warriors managed to stack enough avoidance to become unhittable. At that point DKs could be 2-shot, which made them markedly inferior (and honestly unusable) tanks.
Man, it's a good thing Blood Legion, one of the top WoW guilds in the WORLD doesn't use a blood DK to tank every HM in FL...oh wait.
Back on topic, to some of you saying that the 5% buff to Unholy Might is a direction damage increase, sorry, but that isn't the way it works. It's a 5% buff to strength. The only thing that increases damage by a flat 5% is..wait for it..a 5% damage buff.
Having played dps'd as a DK since the beginning of Wrath, I am disappointed with the state of DK dps in general. Your choices in spec (and playstyle) are either 1 spec that relies HEAVILY on several procs (frost) or one spec the relies heavily on buff management and a proc (Unholy).
Both playstyles are fun to an extent, but I am a little tired of hearing "Unholy Single Target is fine. AoE needs buffed. Simcraft said so." Here is the problem with Simcraft numbers. It's in an ideal environment. No one really pays attention to this, but most of the time, when giving out numbers, sights like EJ et al give numbers based on a "Patchwerk" style encounter, with ideal proc rates on talents/trinkets, etc etc.
No one really pays attention to helter-skelter numbers, but they are there. That is the only time you will actually see Unholy outperform Frost. This is for obvious reasons, such as stronger diseases and pet damage.
Here is the true problem with all this, you can say that single target is fine, which to a certain extent it is. Unholy (in my own personal testing) is about 1k-1.5k (1.04%-1.07%) behind Frost in practice. The problem is, as haste and weapon speed scales with upgrades/raid size, Unholy falls farther behind.
Another big issue is that most people don't play Unholy in a raid setting. Most of you (after a cursory glance over your armory and guilds WoL pages) haven't played unholy in a long time. This means that you are using numbers based on Simcraft, which at times can be flawed or raidbots, which if you look at the data they are pulling from, can be skewed based on bugged logs being uploaded or people starting logs late in a fight.
The real issues facing unholy are things like Matron said. Crit and mastery being applied to ghouls AND the fact that the only way to ensure that your gargoyle does the right attack, is to "twist" him.
Another big issue is SS damage in general. It is nowhere near the damage 1 OB does, even if you add in SS* damage. Anytime that an AOE spell (DnD) should be used over a single target attack (SS), there is obviously something wrong, imo. Also, the reason why unholy has a ramp up time is a two-fold problem. First, the classes mechanics (read: RotFC) and trinket procs hinder burst damage out the gate. Secondly, to add to that frustration, Unholy is based around Disease/DC/DnD damage, which is only does it's best damage from..you guessed it..having the most strength you can at any given time.
*Edit: Meant to say: "...even if you add in SS Shadow Damage portion."