oda rushed the fight because it was a flashback but the fact Kaido still has PTSD about him and respect his strength should be telling
Still, overestimated.
His showing towards roger and WB showed he was lvls below them.
Oden´s strongest attack did nothing, but a scar against a non prime kaido.
If a man´s strongest attack can only give you a scar while your attack can permanently defeat him, you are stronger, it´s simple as that.