PvP is impossible to balance. I said that as far back as vanilla. The problem is the ELO style rating system sucks. That needs to be fixed. Instead, hand out rewards based on best rating for every possible comp. the best rated team for priest / war / rogue gets glad. The best rated team for priest / priest / priest also gets glad. The best rated team for dk / shaman / warlock gets glad. That will make for a lot of glad but who cares. Blizz can post leaderboards for every class comp. balance becomes irrelevant because you are only competing for glad with your exact class comp.
It may sound dumb at first but you actually fix balance issues.
They can hold a quarterly arena tourney if you want to see different class comps duke it out.