Game balance is a very frequent topic when it comes to WoW. With every nerf or buff, there comes a vast explanation from the player base as to why it was and was not justified. Perhaps one of the most common lamentations regarding a nerf that we see is when Blizzard "nerfs PvE for the sake of PvP." While Blizzard does make PvP damage adjustments from time to time, there are far more damage changes that are made due to PvE concerns than there ever has been for PvP. It's an easy fallback to take up; blaming the aspect of the game which you don't actively take part in, yet it would be far more accurate for PvP players to complain about PvE.
There's another trap that's easy to fall into: that PvE balance is easy to do. To be fair, balancing against Patchwerk encounters isn't that difficult, although you'll still never get it perfect, but WoW has only had a single Patchwerk encounter, and that was Patchwerk. For all the damage juggling that Blizzard does, the largest factor in game balance is always going to be the encounters themselves. Each fight has unique mechanics which mingles with the way specs operate and it is that which determines how a spec fairs just as much as any damage balancing on Blizzard's part.