Post-BC, linear progression (getting harder the farther you go) works up to a point. Overall, Karazhan is easier than the beginning 25-man raids like Gruul's. Sure, you might flip around specific bosses, like doing Void Reaver before Al'ar, but most bosses are set up to be completed in a line of progression, even if it's forced by way of geography. So extending this idea to current raiding content, you would expect Tier 4 content (Kara/Gruul/Mags) to be easier than Tier 5 (SSC/TK), which in turn is easier than Tier 6 (MH/BT).
Looking at WoWJutsu and from my own experience, this really isn't the case. The first boss you come to that's out of line with the gradually increased difficulty is Magtheridon. While about 57% of all raiding guilds have killed Gruul, only 32% have successfully downed Mags. The number of progressing guilds jumps right back up to 35% of raiding guilds grabbing lewts from Lurker because while Magtheridon does drop T4 chest, you can easily bypass him and his annoying cubes. The math shows there's little keeping people from T5 once they've gotten Gruul under their belts.
Examining the transition from T5 to T6, you'll see a similar but more extreme picture. About 21% of all raiding guilds that have beaten Leo, only 12% of guilds have defeated Vashj. This means about 43% of guilds that are working on Vashj have yet to move past her. It's even worse when you look at Kael, who drops the last piece needed for MH attunement. About 21% of all raiding guilds have downed Solarian, but only 9% have continued on to "kill" Kael. In other words, the difficulty of Solarian to Leo is nearly the same, but Kael is much harder than Vashj, even. About 57% of guilds on Kael have yet to get their vials. The difference here is you HAVE to kill these bosses to gain access to T6.
But both WoWJutsu info and experience have shown that once you get your foot in the door to MH/BT, there's little keeping you from beating the game. There is only a 2% difference between the total number of raiding guilds that have beaten the first and last bosses in MH. In Black Temple, the separation between Naj'entus and Illidan is roughly 4%.
You can also look at it as a matter of time to progress. It took my guild 4 months to clear SSC and TK's 10 bosses. MH and Black Temple's 15 bosses only needed 3 months of work. Note that we were downing a couple new bosses per night on the early T6 stuff and Illidan only took 2 weeks of serious attempts to master. We're a pretty average MH/BT guild, too. There's tons of other guilds reporting the same thing.
So what does this mean for raiding? Well for one, it means that T5 to T6 progression is still unbalanced. Over the past few patches, Blizz added additional tier drops to all bosses, nerfed Kael by reducing the health of his advisors and completely changed the Solarian fight, no longer requiring tanks to wear dresses. They have also introduced T5 level gear available via heroic badges, with the idea that guilds will be better geared before they hit Vashj and Kael. It was also to fill some gaps that the SSC/TK gear didn't cover.
I would argue that they still haven't done enough. If half the guilds on a medium level boss can't get past him, to the point he's earned the reputation as a "Guild Killer", there's something seriously wrong. If it was gear, then the heroic badge items should have helped, and perhaps they did on some small scale. But by all appearances, Kael and Vashj are still major tuning errors on Blizz's part.
Blizz has also worked themselves into a corner with the attunement situation. So far they've completely nixed the attunement requirements for TK and SSC, after Black Temple came out. Progression through those instances looks good, so that's worked out well. But with the ease that guilds are blowing through MH/BT once they get there, there's no way they can lift the Curse of the Vials. As soon as that happened, there would be no reason to even fight Kael or Vashj. And in my opinion, the early MH bosses are even easier than Karathress. With no vial attunement, you'd do about half of SSC and a couple of bosses in TK before you moved on.
So what you have here are thousands of raiders who are playing to explore end-game content, the majority of which will get trapped under a glass ceiling. What do you think Blizz should do about it, if anything? Should MH/BT continue to be artificially elitist? Do you think the Sunwell will allow Blizz to make some serious changes and open up the far end-game raiding content to more players? Do you think there should be attunements at all?
Marcie Knox has been raiding for a coon's age. It's all she's ever wanted to do and would be lost without the 4 nights a week where she can help put bosses in their place. You might know her from the Raid Rx column, but then again, you might not...