DoTs are unusual spells -- as the name suggests, they do their damage slowly, over time. And while several classes have DoTs that can supplement their regular damage (Priest's Shadow Word: Pain, Rogue's Deadly Poison, Warrior's Rend, Druid's Insect Swarm, etc), Warlocks are the only class who can use DoTs as a viable primary damage source. A single DoT's damage can be shrugged off, but when a Warlock throws all available DoT's on you, their tiny ticks of damage start to add up to some major hurt.
A problem seems to have arisen in part because Warlocks are capable of relying entirely on their arsenal of DoTs and in part because DoTs scale very well with damage gear. A Warlock's ability to cause massive, and deadly, amounts of damage that takes them only several seconds to cast (most DoTs are instant-cast, though their damage is spread out over a longer period of time) to a target that's perhaps moved entirely out of range. Blizzard seems to think that Warlock damage is simply too high (this change does hurt others as well, but as I've explained, Warlocks are the only class that are capable of fully relying on DoTs for their damage), and needs to be toned down a bit.
But to Eyonix's claim that "each new tier of equipment adds to the amount of damage DoT abilities have, yet that damage is not mitigated through combat ratings found on typical equipment," I argue that each new tier of equipment also doesn't mitigate the damage caused by all of the Frostbolts that don't crit or the 70% of the time that a Rogue isn't critically striking me. While I could understand an argument that said Warlocks are simply doing a bit too much damage right now and need to be brought into balance with the other classes, this phrasing doesn't make much sense sense to me. All non-crit attacks scale with gear of some sort (be it attack power or spell damage), and none of those attacks are modified by resilience.
So why is resilience being brought in to fix this problem? If DoTs themselves are the issue, it seems to make more sense to alter the DoTs themselves instead of changing an anti-crit ability into an anti-crit, anti-DoT ability. Blizzard certainly hasn't explained their motivations here, but despite that, I have a guess at what's going on here:
Blizzard wants to moderate Warlock damage in high-level PvP encounters without hurting their PvE abilities.
And that's exactly what a chance to resilience will do. Monsters don't have resilience. Low-level PvPers don't have resilience. By not altering the DoTs themselves, Blizzard maintains Warlocks' current strengths in PvE and lower-end PvP. If this is, in truth, what they wanted to do, perhaps it's not such an inappropriate solution.
Now, finally, let's look at what type of impact, precisely, this change might have on Warlocks participating in high-end PvP situations. Eyonix has told us that resilience of the future will reduce DoT damage by the same amount that it reduces critical strike chance. This means that for every one point of resilience your target has, your DoT damage will be reduced by 1%. At level 70, it takes 39.4 points of resilience rating to equal a single point of resilience -- so to do any further calculations, we'll have to have a better idea of the amount of resilience found on high-end PvP gear. For a sample, let's look at the resilience found on the Arena Gladiator sets (rounded to the nearest tenth):
- Druid: 151/160/159 resilience rating, or 3.8/4.1/4.0 resilience
- Hunter: 142 resilience rating, or 3.6 resilience
- Mage: 161 resilience rating, or 4.1 resilience
- Paladin: 161/159/35 resilience rating, or 4.1/4.0/.9 resilience
- Priest: 172/175 resilience rating, or 4.4 resilience
- Rogue: 161 resilience rating, or 4.1 resilience
- Shaman: 167/160/160 resilience rating, or 4.2/4.1 resilience
- Warlock: 160/161 resilience rating, or 4.1 resilience
- Warrior: 144 resilience rating, or 3.6 resilience
Of course, the Gladiator sets are only 5-piece, so players could supplement these numbers with additional gear -- not to mention gems and enchants. However, the stats on what's currently the best PvP set in the game don't worry me very much. Looking at the worst of the resilience stats from above, we're only seeing a 4.4% damage reduction. Let's look at the highest rank of Curse of Agony, for example, which (base) does 1356 damage over 24 seconds. 175 resilience will reduce CoA's damage by 4.4%, or 60 damage (rounded up). In the grand scheme of things, the reduction sounds pretty minor.
So, yes, I'm encouraging calm -- while this change doesn't help high-end PvPing Warlocks, it's not really the massive nerf it's being made out to be. And if you don't PvP (or don't PvP at high levels), the change shouldn't bother you at all.