If Zoro was thrown into the sky with one of his arms restrained and still recovering from a previous attack, he'd be a stump if he took multiple Kiku-chopping slashes all over his unhardened body.
The attack wasn't targeted at Zoro and was a glancing AoE while he was standing and prepared in stance.
DRUNK Kaido TARGETED the slash against Luffy when he was AIRBORN, and Luffy is casting it away with one arm, despite all of the worse factors at play.