There was a short discussion on our forums regarding the difficulty between 10-man and 25-man raids a few months before Cataclysm where I posted the following:
Even though I have faith that the dev team knows how to make 10s hard, I have a feeling they don't really want to go there. The hard stuff would have to be brutally tightly tuned, limiting the experience to even fewer people than in 25s. Harder than now - definitely - but I simply don't see a lot of benefit in going all-out, and I doubt they do either.
From the looks of it, they did go there. This post isn't really about tuning per se, and I don't have enough personal experience from 10-man heroics to really comment in-depth on that anyway, but the encounters seem to pose a good challenge based on the (unreliable) rankings at wowprogress.
I won't go too much into the possible reasons why the top 25-man guilds have 11-13 bosses down and 10-man guilds only 5-6, but reading threads and discussing people, there's one point that is interesting and very relevant for what I'm about to write.
10-man heroics are very setup-dependent, and the favorable raid composition changes between bosses.
This isn't all that surprising, really. As a response to these threads, I started thinking how I'd run a top 10-man group. I'd probably have around 15 people, running two or three characters each. Regardless of whether a top 10-man guild should be expected to do that, or how it relates to the logistics of 25-mans, I don't think there are any 10-man guilds out there that are putting that kind of effort into their raiding roster.
On the other hand, the top 25-man guilds get this flexibility essentially for free if they decide to venture into 10-mans. Logically this would mean that strict 10-man guilds will be run over in the bracket if top guilds primarily competing in the 25-man bracket start viewing 10-mans as a completely equal substitute. This would mean a replay of WotLK, where strict 10-man guilds had to deal with inferior gear and a rigid setup. This time there is less gear difference, but the flexibility in the raid setup is even more important.
Many people have interpreted Blizzard's removal of distinction between raid sizes in achievements and loot, and closeness in difficulty to mean that 10 = 25, so let's stick 'em in the same bucket. I even see people announcing their kills without specifying the raid size.
Do we really live in a wonderful world of balance where Theralion & Valiona are equal in both 10/25? How about Al'akir? I don't know how well as a whole 13/13 10-man would relate with 13/13 25-man in difficulty, but let's face it: the balance isn't there for individual encounters, and it goes both ways. Nor do I think it will ever be close enough on every single encounter. I'd feel degraded if I had killed V & T in 10-man before the fix (or hell, even after it), and no one thought it was even newsworthy because it was the "world 50th" kill. Likewise my eye twitches whenever I see comments about 10 = 25 on the subject of old Albert over the skies of Uldum.
Aside from bruised egos, is there really harm from this? I say there will be, and not for the benefit of 10-man guilds.
The fact is that if the majority of people start accepting this encounter-agnostic 10 = 25 thinking at some point, the top 25-man guilds raiding for first kills will have to incorporate raid size changes into their overall strategy. I know Ensidia explored that at the start of this tier (and probably regret it the moment they found out they couldn't change back to 25), but based on my talks with people, many of these guilds do not view it as a real alternative. Yet.
The more the raid sizes are shifted to the same mental bracket, the more of a real alternative it becomes to get the first kill in the easier difficulty setting, whichever that might be. If that's 25 - tough luck 10-man guilds. If it happens to be 10 - tough luck again, large guilds will figure out an optimal setup and pool gear. It also spells more logistics and gambling for the larger guilds, as you will have to commit yourself to that raid size for the rest of that instance for a week.
Frankly I'm surprised that the people raiding 10-man heroics haven't been louder at the fact that they're getting no recognition for their kills. Based on the pattern we're seeing, they're also unlikely to get any in a while, since every "world first" has already been taken. In another raid setting. Apples and oranges, conveniently equal - too bad for the oranges.
If people started treating 10 and 25 both equally worthy of recognition and publicity instead of jamming them in the same bucket, the raiding game would be a lot better off for guilds of both sizes. There might be the occasional invader from 25 to 10, but the motivation to do so would stay at a low level with the way lockouts work now.
I think defeating truly hard encounters will always earn recognition, regardless of raid size. Now, if only I was informed about all of those and had the means to track them...