I agree but Oden’s been wanked as special all flashback with roger and WB and everyone of note sucking his dick. Kaido kept on mentioning his haki specifically, at first we thought he meant advanced coa but apparently not since according to this summary, he mention that he could see the shadow of Oden(again) but that he can heal this stuff just fine.
Only Oden’s attack(and thus haki) made him unable to heal fully. And what do you know, one of the swords he was using that’s known for absorbing haki and being cursed is in zoros hands. You can’t tell me that this all doesn’t connect mate.
The conclusion i made from it was that Oden was just that much stronger than the Scabbards and therefore his attack power was strong enough to permanently scar Kaido.
Plus I don't give the credit to the sword, but rather the user since Oden used 2 different sword to cut Kaido at the same time. I will always attribute a swordsman's feats to them, rather than their swords. Like I wouldn't expect Brook to replicate the same feats as Mihawk if he was given Yoru.
Albeit in this case, Enma is a special sword in regards that not anyone can use it and that it must be tamed. But that just means the swordsmen able to tame it are also special.
And we've also seen similar stuff like this (obviously not as extreme like draining haki out of one's arm) with Sandai Kitetsu for example. Zoro's 'luck' vs the blades 'curse'.