Kaido extreme defences are most likely due to
1) his df, Luffy said he can not go past his "tough scales" and since humans do not have scales but dragons have that is most likely from his df.
2) Possible he is the one, or one of the few/many, who got the ope ope no mi operation and so he is immortal/invulnerable. This would also explain why an human df user with the hobby of suicide never thought of throwing himself in to the sea and die. Even if maybe at this point that notion (suicide as an hobby) can be forgotten.
Also the wound Kaido get from Oden was quite serious, let's say it is comparable to the one Luffy got from Akainu or the one Zoro got from Mihawk and while Luffy and Zoro were, rightly, uncapable to even move right after the blow Kaido on the other hand managed to go back on his feet and attack Oden. Of course his myth (110% awakened) zoan is a big portion of the explanation to this but this thijg was big and imo something else (like the ope ope operation) could fit in as well. That or Oda had to run and end the flashback asap so he skipped any non useful panel aka make him take a huge blow and regenerate in the span of a few panels.
