Simple fix to that: All Frost spells deal 15% less damage to players (including Waterbolt). Stacking debuff is now removed; all Frost spells are increased by 20%.
Boom. Took me two seconds to come up with that shit.
That, or just remove our worthless in PvE/OP in PvP Mastery and replace it with something balanced in both...? Yeah, there's a nice thought.
They just put little to no effort into coming up with something balanced and come up with a quick fix that ends up making someone (PvE players atm) unhappy with a stupid bullshit change.