There's a significant side effect of the Agility change for plate tanks, however, and even though it's possible that the increase in Parry from Strength (to 27%) was intended to offset the damage, this will remain a substantial nerf as-is.
In Cataclysm, Battle Shout (Horn of Winter, Strength of Earth Totem) went from being a completely terrible buff that no one cared about, to a very significant buff for both tanks and dps. Currently on Live, it provides a variable buff of about 1.7 to 2.5 percent avoidance, depending on diminishing returns and the class of the tank. It is one of the rare few buffs that actually matter to tanks, and it is nice having a buff from someone else actually be important (the only other external buff that substantially reduces physical damage taken is Inspiration/AF).
The 4.2 change, while serving the legitimate purpose of making Agility gear undesirable to plate tanks, also brings with it a significant nerf - plate tanks will be losing the dodge portion of Battle Shout avoidance. The harm that this nerf will cause will vary - Druids will be completely unscathed, Paladins will be hit the worst since Paladins currently get more benefit from Agi than other tanks. In addition, lesser-geared and newly-85 tanks will be hurt moreso than high-end tanks due to Battle Shout being a flat buff.
I realize that not everyone might understand just how important Cataclysm Battle Shout is to a tank. So here are some numbers -
My warrior (368 equipped, 13/13H and fully heroic raid geared)
- 33.43% total avoidance unbuffed, 35.25% with Battle Shout + Mark, a gain of 1.82% (1.02% dodge, 0.80% parry)
My druid (353 equipped, does not raid)
- 40.17% total avoidance unbuffed, 42.42% with Battle Shout + Mark, a gain of 2.25% (2.25% dodge)
My paladin (341 equipped, new 85)
- 26.84% total avoidance unbuffed, 29.27% with Battle Shout + Mark, a gain of 2.43% (1.56% dodge, 0.87% parry)
The current version of Battle Shout gives a roughly equal amount of avoidance to all three tanks once diminishing returns are accounted for. Unfortunately, the 4.2 change will take away the dodge contributions of Battle Shout from the Warrior and Paladin, making it a 0.80% and 0.87% avoidance buff instead of 1.82% and 2.43% respectively. At the same time, the druid continues to retain a full 2.25% avoidance. The 4.2 patch is already providing a fairly-large, separate buff to Druid tanking, as well as a nerf to Paladin tanking, so I don't feel like a disparity in avoidance from buffs is warranted on top of that.
The change in Parry from Strength does very little to make up for this. It hurts lesser-geared tanks progressively worse, as they don't have gigantic amounts of Strength to make up for such a large loss. My Paladin stands to gain 53 Parry rating, a paltry 0.20% avoidance. My heroic raid-geared Warrior will gain 81 Parry rating, about 0.32% avoidance. Both of them lose a considerable sum of avoidance, while the Druid loses nothing. While I understand and respect that different tanks are different (and should have differing amounts of total avoidance), I don't feel like Battle Shout of all things is the place to differentiate them. There currently isn't a disparity, so I don't feel like there suddenly should be one.
There are several ways to solve this disparity, while still keeping the desired outcome of Agility gear being undesirable to plate tanks. One method is to make it so that Agility from sources that are not gear (Battle Shout, Mark, flasks, Tol'vir pots) will still contribute to dodge for plate tanks. This seems like it might be complicated and difficult to hotfix in time for 4.2, though that doesn't rule it out as a future solution. Another method is to give Battle Shout/Horn of Winter/Strength of Earth Totem a flat, undiminished 1% parry chance, to make up for the avoidance that plate tanks are going to be lacking. There is a precedent for this (Rune of Swordshattering), and the only side effect of this change is a meaningless, very minor avoidance buff for rogues, hunters, and enhancement shaman. Such a change would mean Battle Shout gives my Warrior, Druid, and Paladin tanks 1.80%, 2.25%, and 1.87% avoidance respectively (instead of 1.82%, 2.25%, 2.43%), which combined with the Parry conversion change would mean the Paladin only loses a tiny sliver of avoidance, instead of a very harsh drop. It doesn't quite eliminate the disparity between Druids and non-Druids at the new-85 level, but it does reduce it to the point where it won't be a big, confusing hole. This change seems like it might be easier to hotfix in before 4.2, to do something about the problem before it occurs.
It's my hope that something is done about this before 4.2 actually drops. Battle Shout is an excellent buff for tanks, and I don't feel like plate tanks should be punished this severely just because a few top-end tanks decided to go for Agility gear. Thank you.