Actually the real problem is bringing down burst dmg only from SOME classes, whille lets say frost mages can still drill you a new one on pretty consistent base. I'm quite positive that even with nerf to chaos wave MLS/MLD will remain top tier setups becouse mages will carry, but what made me drop my lock was affliction state i expirienced firsthand in beta - malefic grasp simply destroyed spec outside of pve setting, before affli lock even being focused (everybody likes to focus locks anyway) could apply serious preassure on oposing team whille now it's almost non-existant if you aren't chaining MG.
In result from caster with great sustain dmg/support utility locks got gimicky cd-based burst spec. And obscene burst always result in nerfs. Was this nerf justified - certanly yes, have blizzard done a good job in fixing pvp problems in 5.1 - no. I've a feeling Blizz is only capable of bandaiding pvp problems and that only leads to more problems.