A fight like Lady Sinestra is of course intended to be very hard at the current gear level. It's a punishing, unforgiving fight designed to make player choices and strategies more important than gear. Hard-mode fights are always designed around the idea of giving the players what they say they want -- that is, a real challenge that they have to overcome with skill and proper play.
The upside of this is the emotional satisfaction you feel when you overcome such a challenge. The downside is that this is institutionalized elitism, deliberately so, and that means that the pool of people getting in to see the encounters and test them is limited. The more players running content, the more quickly bugs and exploits can be discovered and addressed. Of course there's internal testing, but no two raid groups think alike, and Blizzard's internal testing isn't always going to reveal what a group of experienced, skilled raiders will discover, much less when you have hundreds of raids going on at any given time. We all remember people using trinkets to push C'thun's stomach acid debuffs off of themselves.
With an encounter like Sinestra, there simply isn't that body of raiders running the encounter. There can't be. At the time this encounter was defeated, only one other guild could even get in to see her. This is to a degree the price we're going to pay to have these kinds of selective, elite encounters intended to provide a maximum of challenge. While it had to be maddening for <Paragon> to be using a strategy on one attempt and have it not work for the next because of a hotfix, there's probably not much else Blizzard could have done.
What's even more interesting is the fact that Blizzard was, in fact, watching <Paragon>'s attempts and making hotfixes like this. <Paragon> and other world-first guilds are therefore basically becomes a kind of extra stage in the beta testing process. If you can't allow a lot of people in to test your selectively elite hardmode-only fights for fear of details leaking out, this becomes how those encounters get their full shakedown. In essence, <Paragon> is the Hal Jordan of Lady Sinestra encounters. It also means that future encounters will be designed deliberately to be challenging, based on the experience of designing and then observing world-first guilds beating these encounters. It becomes interactively iterative. That's the closest I've ever seen to WoW having user-designed content, in a way: It's user-defined content, content evolved to the standards set by this group's work to beat the previous content.
So if you're a hard-content-focused guild, take heart. The next hard mode you face? Blizzard may well design it after having watched how you beat the last one.
World of Warcraft: Cataclysm has destroyed Azeroth as we know it; nothing is the same! In WoW Insider's Guide to Cataclysm, you can find out everything you need to know about WoW's third expansion, from leveling up a new goblin or worgen to breaking news and strategies on endgame play.