Balance hasn't been particularly good, but honestly no better or worse then most other seasons. There have absolutely been massive improvements, things that people have been asking for for years that were just ignored until now.
*Region wide arenas
*First expansion not dominated by pve gear
*Conquest point catch up
These three things are massive, not to mention Holinka, having a dedicated pvp "dev". and blizzard flying out the top players to discuss balance.
MoP has its problems, warriors, hunters, and mages have been ridiculous for the entire expansion. That's not to say imbalanced classes are acceptable, but it is expected. Rogues/warriors/druids/warlocks in BC, DKs/hunters/pallies in early WOTLK, prot class/wizards in late wrath. rogues/shaman/warlocks in cata. Balance will always be an issue, but the difference between MoP and every other expansion is they seem to be making a real tangible effort with the arena community, though it may be too late at this point, they're still trying.
Poor defensives trollface.jpg just because your class is killable along with every other class in the game you do not have poor defensives, you can cycle through Skin, Ursoc, bubble/disperse, wall, heart, running at 300% all game