The upcoming changes to block in Cataclysm have got me thinking about how they'll impact the game recently, and there are a few points I thought might be interesting to discuss.
Just to recap, Blizzard is planning to change the Block stat in Cataclysm to mitigate a percentage of damage off an incoming attack, rather than a flat amount.
Now at first blush, this seems like a great idea; as it is right now Block is practically useless in high-end raiding, and way overpowered in things like 5-man instances (Prot Paladins, I'm looking at you). This dichotomy is impossible to solve with Block in its current state, though fortunately it's not really a balance problem - heroics are pretty faceroll, and a Warrior/Paladin tank can avoid Block on their gear without any avoidance/mitigation penalties.
Naturally Blizzard wants to change Block to make it an interesting stat for all involved, and Cataclysm is the perfect place to do it. While changing it to a percentage-based mechanic seems like a good change, the more I think about it, the more I see it causing all sorts of balance issues.
Primarily, I'm concerned with two things: damage intake, and health stability. There are two ways Blizzard can balance these: Block tanks have identical avoidance to non-Block tanks (without factoring in Block), or Block tanks have less avoidance than non-Block tanks. Let's look at each of these in turn.
Balancing things this way seems rather silly, all things considered. If a Warrior and his good friend the Death Knight both have the same avoidance levels, but the Warrior has Block, well, that Death Knight is getting benched. Not only will the Warrior take less damage overall (Block is damage reduction!), but he'll also have more stable health, due to Block evening things out a bit more.
So the obvious solution to the above problem is to make Block tanks just have less avoidance overall, right? Let's try making damage equal once you factor in block. So we have a Death Knight with 50% damage reduction post-DR, and a Warrior with 30% chance to block for 30% damage reduction. The Warrior should then have 44% damage reduction after DR and before Block to make things average out.
But wait a minute. If both the Warrior and the DK take the same amount of damage overall, but the Warrior "avoids" damage in a more stable manner due to Block, then the Warrior is just going to be better. Having a 30% chance to take 30% less damage is easier to heal than having a 6% chance to take 100% less damage. Statistically speaking both will take the same damage, but the Warrior is going to take that damage much more steadily. You've basically got an artificial EH boost from a healer perspective.
So from here, one solution would be to make Block tanks take more damage throughout the course of a fight than non-Block tanks. It's hard to call this one, but I think you'd see the non-Block tanks dominating Block tanks. Keep in mind that every fight has to be tankable by a non-Block tank. Your healers will be able to keep up a non-Block tank, and at that point then the tank that takes less damage is clearly superior.
So working through all this, is it possible to attain a reasonable balance between Block/non-Block tanks in Cataclysm with a percentage based block stat? I don't know that it is. What do you think?