JeffKretz, that sort of sounds like me(the healer; I was the only one geared in a team finder group) but our group went differently. We told our tank to bring Malgus to the edge about THIRTY TIMES and he didn't understand even after we showed him exactly where to go. We wiped four times because of him and then one of our DPS' left. After that I gave up too. Some people just shouldn't play tank class, to be honest. I don't dislike people who can't play a certain class though; not everyone is good at everything. /End Rant
As for coping, I got in a group for Lost Island and our second Sage(me being the first) was assigned as DPS even if she thought she signed up as healer. She re-spec'd and rolled with it. And guess what? We got through Lost Island, one shotting every boss but the last one. It was damn fun too.
The sad thing is, a few weeks later the same thing happened to me. I got placed as DPS in Lost Island and a bunch of people in my team had hissy fits, spitting, crying and saying we'd never make it through because of having a DPS Sage.
It's sad to see some experienced players unable to accept that not everything needs to be perfect to work.