Jozu is a YC2, the slash was not aimed at Jozu, who has a df designed to counter swordsman, but he was still bruised
You have to aim to cut diamond, similarly to steel, Mr 1 hints at it here
This is what happened when Mihawk aimed at Luffy
This when Mihawk knows it's Daz
Aokiji only managed to do so with a distraction
Before that Jozu gave him a bloody lip and fought with him until the distraction
Vista is YC3 in the WBP, Ace was not a YC2 level fighter, and he threw himself in front of Akainu, Akainu also had a df advantage
Vista is YC3, Kizaru did nothing to Marco until the distraction
Marco overpowered him in the first clash