Guild hasn't attempted Arch yet. We got 4/5 and moved on to BT while folks farmed their PvP trinkets. We leave Hyjal's first four as farm content right now while we progress in BT, and we ought to get Gurtogg down soon. (Should have been last week, but since it wasn't, it's frustrating it won't be this week either thanks to the patch, which killed our Tuesday raid and saw us bringing in some noobs for recruiting now that we can without attunement last night.) This is just to explain where I'm coming from.
I don't know about other fights, where I can at least learn to do my thing while everyone else is doing their's, but I have great issues with the Gorefiend fight. There is no way to practice it, it happens randomly maybe once per fight, it uses controls that you are not accustomed to...while I wouldn't be the least bit surprised if some day I start getting sat on that fight because I simply can't do it, I'm extremely frustrated by this because it's not like I'm usually the one hurting the raid and I'm also usually very good at mini-games in most video games. But this one I cannot do.
And please don't suggest the "simulator" to me until you can find one that actually works in a web browser other than Firefox. I'm not putting a second web browser on my system so they can fight each other for priority just so I can run some applet.
To the OP, I do have one question, though: Are there no other fights your guild has encountered before where this was the case? Hydross? Leotheras? Supremus? To a limited extent, Void Reaver?
I hate to say this, especially since it will look like it conflicts with what I said up above, but I have been guilty of this from time to time. It's very easy to just put your head down and do your thing after feigning a few times early on in the fight. When the tank has a 50k+ lead on you, you don't expect it to matter intensely that you feign every 30 seconds, and it's hard to get a rhythm for shot cycles if you interrupt it constantly. But I'm often the person with the highest threat below the tanks towards the ends of fights as a result. Once in a great while that comes back to bite me. At 29% on Gurtogg sounds like something I might do...once.