Something a little more convenient, like a single button? There are times when you get aggro and mobs are all over you, so you'll want to kite and dodge around while trying to leave group. A little irritating to have to do the right-click and select from menu.
Something like a EJECT level on a fighter jet if you will.
You can't use exit area while in combat. You should be booted form the area if you /leave, I have no idea if you can use that during combat as I have never tried to do it. You could always /stuck and then exit area.
A word of advice though, if you become known for quitting an FP while in the midst of combat you are going to end up on a lot of ignore lists. This will make it pretty tough for you to get queues in the group finder. In the situation you described above I can only think of a few things that could make all the mobs attack you as a GS:
- You pulled them. That's your bad not the groups. Be more careful next time.
- The tank is dead. That's either the tank or the healers bad. Unless it's happening on every pull there's no need to quit the group.
Most story mode FP's are easy enough to get through if you keep plugging away at them. Try sticking them out a little bit more often. The stories in the FP's can be pretty good too.