I'd say he was that strong to scar Kaido it was his strongest attack and we seen with the Scabbards you don't need AdvCoC to injure Kaido.
It makes no narrative sense for Zoro to be pulling off advanced CoC techniques pre-timeskip when just recently Zoro has just only drew out his latent CoC power with Enma forcefully sucking haki from Zoro.
The manga is clearly showing that it is Enma that is pulling the AdvCoC out of Zoro so him being able to do that (Asura) without Enma makes no sense either.
Never said you need ACoC to injure Kaido. Just like Luffy was hitting him with ACoA and Scabbards + Zoro with Ryou their attacks were too shallow.
Fact is that Oden who managed to scar Kaido was using ACoC. Scabbards couldn't scar Kaido. Zoro could. So Zoro is most likely using ACoC. Or maybe ACoA that Scabbards couldn't but we also not sure about Oden using it.
Never said Zoro was using ACoC pre-timeskip. We have basically 3 options, either Ashura is CoC(not advanced) and Zoro used ACoC with it or Zoro just unlocked his CoC now and we still have no clue of what Ashura is then he may or not used ACoC with Ashura.
Enma isn't pulling a shit from Zoro. Zoro is releasing all he got. He was drawing back because of Enma. He never needed that stupid sword. WTF you said about Zoro using Asura without Enma makes no sense? He did it at pre-timeskip twice.