Just make vulnerability debuffs more prevalent throughout the game's dungeons , both in boss fights, such as unavoidable damage granting vuln stacks too, and from generic trash. Gear will still be just as relevant, but mass pulling will be riskier and healers will definitely be more distracted.
Everyone happier (except maybe tanks trying to fight in gear 20 levels below their current level and the healers trying to keep them alive in those cases) and not a single class modified.