Balance doesn't really matter. Not every class and spec is supposed to be viable. It's always been like this. In fact, comparing to previous seasons, current class balance is ok-ish. The real issue with this season (and I personally believe, expansion as a whole) is how boring it is due to bloated spellbook, enormous amount of instant cc and cooldowns, one-shot mechanics etc.
MoP is just basically Cata 2. Same boring playstyle, more (dumb) stuff. In Wotlk/TBC there was much more emphasis on positioning, situational awareness, and other individual skills. Remember that time when you could feel you were clearly outplaying someone? Now when was the last time you felt you were massively outplaying or getting outplayed and it mattered? Even though class balance in s5 was worse than now, it was by far more fun to play. Boring arena playstyle, plus being forced to do those horrible rbgs to stay competive is what makes this season (and probably whole expansion, just like Cata) less exciting than s5.
Edited by hotcowz, 25 November 2012 - 08:13 AM.