It doesn't matter, Kaido and Big Mom are not talking about Zoro's power, but about Oden's presence in the sword, and this is not related to Zoro's real power.
If Big Mom and Kaido were frightened by Zoro's attack, then the argument that Hiryu Kaen is superior to other attacks would have credibility, but that is not what happened
Big Mom put all the attacks in that chapter on the same pedestal
If Big Mom and Kaido were frightened by Zoro's attack, then the argument that Hiryu Kaen is superior to other attacks would have credibility, but that is not what happened
Big Mom put all the attacks in that chapter on the same pedestal
This doesn't necessarily equate to Oden being a dormant soul or spirit stored inside Enma that has awaken. It can very well mean that the way Zoro is wielding the sword is reminding of Oden.