@Bil02 we don't see which sword he's using on Apoo
Also when Oda shows us that Oden flashback when he's training the scabbards in ryou, he cuts to a hardened sword. There's a black sword specifically after the flashback and then the scabbard use Oden's move
If Oda wants to show that Zoro is using Haki AND FAILING while using Haki, then he'll make it black.
Like if your point is that Zoro's Haki can't cut kaido then show it. Show the blackened swords doing shit.
When Zoro talks about Unleashing Enma, we know he's along about Haki because that's the only thing Enma does.
Also when Oda shows us that Oden flashback when he's training the scabbards in ryou, he cuts to a hardened sword. There's a black sword specifically after the flashback and then the scabbard use Oden's move
If Oda wants to show that Zoro is using Haki AND FAILING while using Haki, then he'll make it black.
Like if your point is that Zoro's Haki can't cut kaido then show it. Show the blackened swords doing shit.
When Zoro talks about Unleashing Enma, we know he's along about Haki because that's the only thing Enma does.
Anyways we've seen Kiku piercing Kaido with zero Hardening,so Zoro the better swordsman can use Ryuo with no Hardening too,you are the one assuming he necessarily didn't when there is no proof either way at this point.
Even in the scabbards' Tougen Totsuka on Kaido,Denjiro's blade is not hardened,then later Denjiro pierced Kaido from the sides again with Zero Hardening so Zoro obviously can use Ryuo with no Hardening.
Now did Zoro use Haki on his strike against Kaido? I don't know but I'm not assuming he necessarily didn't.