The difficulty of WoW is they do not have balance and it is because of the old mindset of PvE and PvP damage was not separated. However, SoD PvP is getting out of control. The issue is, we cannot call for Nerfs because of PvP. So, this becomes the question of how do you balance PvP if PvE is so wildly over-tuned for some classes and not for others.
I think the obvious action is to focus on how did they address Arena’s in Retail, which was to ban certain abilities.
Example 1: Paladins Immunity Bubble is not usable in BGs. How does this solve Paladin issues in BGs? It prevents them from dealing 100% damage bursts with no counter play. But does not nerf their PvE DPS output.
Example 2: Druid (Boomies) Change how their damage is dealt over time instead of upfront damage. Starsurge has its synergies removed from Starfire, Sunfire is instead a dot 100% vs damage upfront and a dot later. Solves some of the Boomie OP, but does not attack their PvE damage.
BGs can incorporate other patches like the pre-patch of TBC which brought DR to CC. The issue with classic and also this SoD is CC is way too powerful. It is far worst than even MoP. Having all CC start at 4-8 seconds, means only in BGs does this happen; but does not change how World PvP works.
BGs need to be where changes happen, not the classes. People want to have montage kill streaks and stuff to flash off how OP a class is in world PvP. But when BGs are the core foundation of honor, we have to look at how can BGs solve the PvP experience. So instead of Nerfing classes because of PvP, change how their damage is done like DoT and focus more on BGs tuning classes instead of devs tuning the classes that affects the entire game.
This is how you can balance the PvP experience without destroying your PvE experience.