There are specs that are good in big fights that are considered good bg specs and those who work better in small fights.
Example: enh shaman in a big WSG fight is close to useless and definetely not something I would want to be pocket healing as it drops too quickly. Enh in arena or small node fights is much better though. Same thing goes for most of the weak bg specs like ele, balance, feral, ret, monk, dh etc. Put them in a big fight and they do nothing compared to what a hunter, lock, priest would do but in a small fight they instantly become a lot better. That's why ret is a wheelchair in bg but one of the top specs in arena or why balance is so good on off nodes rather than in team fight. This is the reason why some specs are so good in duels while not so good in bg. And yes, I know there's that "super good player who always carries on an undergeared DH or something" and how I'm just too bad at the game to realize it but that's not how things work. You either play a good spec or don't play at all.
From what I've seen most people play every class the same way and complain when they get killed by a hunter. As someone who has almost all classes twinked out, I've seen the differences and can easily tell that the majority of specs don't work in bgs. They require a good team and not-so-good opponent to work. You simply can't play havoc and do well in every single bg. Sometimes you die before you reach the enemy. You can play a priest or hunter and you'll do well in every game, regardless of teams. You complain about hunters but I wouldn't want a hunter on my team to be swapped with a DH or balance druid unless it's a very unbalanced game in my favor. Just deal with it and reroll to something that works. If you're tired of enh shaman dying too quickly, roll a fury warr. If you don't like ele sham, roll a warlock. Can't really play an undergeared niche spec and complain about how other specs are stronger and that people prefer to play them. No one in their right mind would roll a niche spec that has 3 buttons at 20 unless he's been playing it for a long time.