Zoro's AP is considerably > Luffy's. An Opper mid tier attack from Zoro forced Kaido to dodge and had Big Mom scared for his life.
Luffy's High Tier attacks were tanked without much trouble.
Pretimeskip, ShiShi Sonson seemed more formidable:
- It was Zoro's finisher vs Daz Bones
- It was Zoro's finisher vs Kaku
Hiryuu Kaen was used against Ryuma, but Zoro beat Ryuma with Nitoryu and while not wearing his bandana.
I think Hiryuu Kaen being so powerful this chapter is because current Zoro is just that much stronger as opposed to the technique suddenly becoming more powerful than techniques it was weaker than preskip.
I place both of them on the same level as upper mid tier techniques for now. They're Zoro's strongest Ittoryu techniques.