it's a mater of choice, when zoro first used that technique he choose to not cut the leaf, jozu just came out of nowhere and blocked a slash that was meant to cut.
A slash that was meant to cut Whitebeard
look at it this way, Mihawk swung at Luffy and his slash cut through a mountain of ice. Then Mihawk swing at Luffy again and STEEL MAN DAZ BONES BLOCKED IT
Are you gonna say Daz Bones just blocked a mountain cutter slash? Because apparently to you, everything in front of Mihawk’s sword should be cut down the same no matter whether Mihawk is aware of it or not
By this logic, Daz Bones is as tough as Diamond Jozu. They both blocked stray mountain+ cutting slashes from Mihawk