About a week ago, Blizzard unleashed a one week warning that the Firelands was going to be hit with a nerf akin to the 20% nerf that rendered all T11 normal content completely trivial. This has erupted into a bit of a fireball in the blogging world. People are drawing lines on all sides. Some are saying that nothing should be nerfed, some are saying that everything should be nerfed, some are saying that heroics should be left alone but normals nerfed. It's kind of a mess.
Personally, I'm looking at the long game here. Consistency should be Blizzards watchword. For the most part since T8, Blizzard has done a good job of putting out content that has been fairly even in terms of difficulty. Difficulty at the bottom of the instance, and difficulty at the top has been fairly consistent; the major tuning factor is one of throughput. Going from Flame Leviathan in 213 gear, to Beasts of Northrend in 226 gear, to Lord Marrowgar in 245 gear, to Halfus Wyrmbreaker in 346 gear, to Shannox in 359 gear isn't a serious step up in difficulty anywhere along the line. Likewise, Yogg+0 in 239 gear, H Anub in 258 gear, HLK in 277 gear, Sinestra in 372 gear, and H Rag in 392 gear, despite more stratification than the opening bosses, doesn't include any ridiculous outliers in terms of difficulty. Content is not getting more difficulty, nor is is getting easier. They're remaining fairly constant. This is a good thing, because it gives people realistic impressions of the progression that they can expect across tiers.
In the same vein as consistency is avoiding creating major skill gaps. Encounters that exist as progression bottlenecks by being significantly more difficult than any of the encounters previous hurt the morale of a group. Going from clearing a new boss each week to be stuck on a single encounter for over a month is a recipe for destroying a raid group. This is one of the reasons why Blackwing Lair was a terribly designed instance. Going from Molten Core where the majority of the bosses were simpler than any five man boss in Cataclysm to Razorgore and Vaelestraz, who were as difficult as Ragnaros, was a huge skill gap. Further exacerbating the issue was that Razorgore and Vael weren't only the first two bosses in BWL, they were the first two encounters. There wasn't even trash you could farm. Because of this, even after the release of BWL, groups that couldn't down Rag had nowhere to go. Vaelestraz got the reputation as the game's first "Guild Breaker" boss. this is the hazard of encounters like Lady Vashj, Kael'thas, Bruttalus, Mu'ru, and Heroic Beasts of Northrend. These bosses all represented significant skill gaps, and raid groups died trying to surmount these obstacles.
Blizzard has also experimented recently with blanket nerfs. Rather than targeted adjustments to bring a specific encounters to the degree of difficulty they intend and letting groups progress at their own rate, blizzard has simply chopped the whole instance down a peg. This began with an adjustment during patch 3.0.2 to all BC raid content, which was justified in that changes to mechanics, specifically group dancing, and multiple potions, made a significant dent in a group's throughput. Perhaps they went a little overboard, but the intent was to counterbalance nerfs to all players. The first true blanket nerf came in ICC with the Strength of Wrynn buff. Starting at 5%, and eventually cranking it's way to 30%, it was built as a means to keep guilds interested in ICC during the longest year in raiding history. The next blanket nerf came when 4.2 dropped, and Blizzard emasculated T11 normal content. Now blizzard has announced it's intentions to conduct another blanket nerf, this time on all T12 content, before the next patch is even on the PTR.
These blanket nerfs give short term progression to groups. However, that progression comes at a cost to the long term health of the game. As I said earlier, consistency should be Blizzard's goal. These blanket nerfs destroy that consistency. Even worse, in destroying that consistency, they create nightmarish skill gaps in between tiers. By the time the 30% buff rolled around in ICC, any competent group could roll into ICC, and push fairly deep into heroics. When T11 rolled around, these same groups expected to make similar process in T11, only to find that without the 30% buff, they're languishing in normal mode for months. This wasn't consistent with the progress they came to expect in T10 content. This frustrated them, and the fireworks flew. Guilds across servers exploded as T11 held a cruel mirror up to their actual ability. Many of these guilds were decent groups that in previous tiers had cleared the instance on normal and pushed into the easier heroics while content was current. However, the time spent in ICC warped their expectations, and destroyed their enjoyment of the game. Because of this, the game hemorrhaged subscriptions a few few months into T11. Blizzard didn't learn from this design failure, and is planning to repeat it again with T12 content.
Inevitably, not everyone will be able to clear raid content when it's current. It takes both skill and commitment, to one degree or another. A less skilled guild that raids for 6 nights a week might progress further than a skilled group that raids, 2 nights a week. But that's because their commitment is much greater. However, the distribution of skill in this game varies heavily, and anyone who spends any sort of time running random pugs in LFD will notice that there are people at level 85 who do DPS that's low by Burning Crusade standards. It's impossible to create content that's capable of being cleared by people that bad, that remains marginally challenging to the current group of raiders. A realistic appraisal of your groups skill and commitment is vital in creating realistic expectations, and realistic expectations are vital for the long term enjoyment of the game. If it took you four months to down nefarian, you should expect a commensurate amount of time to down Rag.
Perhaps Blizzard thinks that the new "Derp" mode, as some of my guildies are taking to calling the new LFR tool scheduled for 4.3, will offset the skill gap. That guilds that made it to 7/7 normal in firelands and 1/7 heroic would be satisfied with being 7/7 derp mode and 5/7 normal. I doubt this is true. Getting inferior gear and no achievements will simply leave them feeling inferior, and still thinking that they're a group that should be raiding in heroic mode. Inconsistency will wound this game.