I doubt there is any game, or any meta game, that does not favorize a certain team composition. At least from the games I have played. The meta game (usually) changes when the game is progressing but since BioWare "balances" only in big patches (1.1,1.2,1.3) it is pretty hard to say its an abuse. It is just better. Move on with the meta, or don't. Thats not the choice of the players you are playing against.
Stealth is a part of this meta game. There are 2 options at the moment, move on and do not change anything or do something regarding tactics or team setup. I have not played enough rated warzones to say something is OP or something is not OP or to develop some tactics that involve something different than sending 1 left and right and the other 6 to mid without having a bad starting situation. You focus a little bit too much on why you lost that game and not how you could improve your tactics in this specific warzone.
I also doubt there is no perfect way to balance 8 classes, where 2 are with stealth and 3 are able to taunt and guard.
In my opinion you should only be able to taunt if you are in tank stance.
Alderaan is in general, in my opinion, a bad designed warzone since win or loss are usually determined way too early. Novare coast is a better design, although I dont like it either.
Also regarding class balance, when we are on topic, our class HAS to be nerfed in the near future. No doubt