DS is Perfectly fine as is. Strong knock back CC that is hard to break, super high damage, ability to combo with other burst. It has and needs counter play to it. Wrecking blow is indeed kind of bad, but it is the secondary effect that should be changed.
The skill would overperform (at least the dizzying swings morph) if it had no cast time. It hits significantly harder than skills that are instant cast and stun, and its particular kind of stun is one of the strongest ones, as it knocks you up into the air, and then down, which takes longer to break than most other stuns. The skill wouldn't have a telegraph without the cast time, and thereby wouldn't have a good counter, which powerful skills need in order to be properly balanced.
"Madness is a bitter mercy, perhaps, but a mercy nonetheless."