For instance, recently while doing Ultima's Bane, I failed miserably as the tank (didn't LB when I was supposed to, LB'd too early, basically looked like a total fail, the other tank never ran this before and did better than me), and everyone else seemed to deal with it .. except for one asshat of a healer, who promptly told me off (but honestly at that point even I thought I deserved it, I stopped playing after that so I wouldn't wither away my own sanity even more).

As for what you did, it was a good thing. A DPS is unfortunately very easy to replace compare to the other two classes, and they don't get much say (try running Garuda EX as a Monk and not get trolled a bit, never ends well for me), this is where someone with more of a say needs to step up, like you did.

If I could give you a commendation for that, I would have.
I think I broke off-topic on this, so I'm going to end it here.