We had a friend, back in vanilla WoW, who played a priest. A shadowpriest actually, but a priest.
Whenever the guild ran instances, they always said, "Where's DB, we need a healer!"
It got to the point that DB stopped logging in because he felt that they didn't want HIM, they just wanted a healer.
He knew better, at least in the case of Boon and myself... because I'd bring my priest if we wanted a healer. But he only had one character that was high level, which was his priest. So we'd always ask him to bring his priest... because that's all he had.
He burned out and left. It was a shame because he really enjoyed the game. But he felt that he never had time to play something else because he always had to be his priest, and he felt that we didn't want HIM, we just wanted a healer.
It's something I hit towards the end of TBC... it seemed I could never bring one of my DPS because I always had to be the tank, because really... do you REALLY want to PuG a tank fo a heroic or a raid? So much easier to PuG a DPS. A good tank and healer combo can make up for a whole host of DPS suckiness.
Sometimes, yeah, it isn't who you are, it's what you bring to the group. People put up with your irritations because they'd rather keep your tank around than have to find a new tank that knows how to actually tank.
Once you know it though, that all they want is your tank... not you... wow, such a blow.
I wish I could go back in time and tell DB some of this. It was him we enjoyed. It was his humor and his wit. He could have been playing a melee-warlock and we'd still want to hang with him.
Miss you, Dawnbreaker.