Luffy's attacks were termed shallow by Luffy himself while Zoro's attacks received visible/vocal recognition every time he landed a hit.
Luffy thought his attacks were shallow cause it wasn't doing as much damage as he expected, and kaido was still dodging those. Zoro landed what? 3-4 attacks? And only one of them had any effect that even lasted a little while. Don't compare zoro's ultimate moves to luffys base strikes and non finishers