Sophus, while the topic title does seem to suggest a dig at Ret, when I read the body of the post, it sounded to me like he wanted to know what he did wrong, and wanted to know if he should be doing something different. My response to him was to address that issue - was his gear OK?
I've also known Ret for a long time, even though I'm not a close friend. I knew both her and her boyfriend from my old LS and was the one who asked them to join FU in the first place (even though neither one turned out to be very involved). Regardless of any player issues involved, the real point at issue I believe the OP was trying to get at was whether he should have done anything differently. Not being in the party or knowing all the circumstances involved, I'm not going to pass judgment on any players. But I can try to answer his question ("Am I doing something wrong here?")
Expecting things to go perfectly in the dunes is just not reasonable at all. IT'S THE DUNES! People die - a LOT. It happens; get over it. People are busy learning their jobs, even if it is their 5th or 10th job, each one is still a little bit different. Or you could be like me, having taken RDM, WHM, and BLM all through the dunes and then deciding to try WAR, THF, or NIN (which I found to be extremely new and challenging). Expecting someone to be GOOD at their job that early also isn't reasonble. It's a learning process. It's also a GAME, for goodness sake. Stop obsessing about getting level 10-20 in one day, much less an afternoon. Set your homepoints, get your asses back up, and get back into it.
So while you bring up some valid points about things players can do to control the situation, nine times out of 10, a link of IT gobs at that level probably will kill your party, no matter what your skill. Expecting to be able to deal with every contingency at that level is much different than expecting it 50+. If you are trying, and keep trying to learn, that's all that really matters.