Lol... They still failed to damage him...
I'm just using your logic
Oden>every top tier
Who said that?
Oden managed to make a perminent scar on Kaido
Giving damage is NOT the same as giving permemant scar
What I mean by that is that Luffy most likely will learn to be able to damage Kaido with his advanced Haki. And that type of haki is something Rayleigh can do at his old age with ease. And many top tiers most likely have it
giving damage then to be healed with time is NOT the same as giving a scar that would last forever
And I think that's what will be Oda's way of giving hype for both:
1- Oden's skills as a swordsman
2- Enma Sword
you see, if by any chance Oda gave the full credit of Kaido's injury to Oden personal prowess and his skill, Enma sword hype would be simply go to waste, cause that's basically like saying Oden would have given a perminent scar regardless of what sword he's got
On the other hand, if Oda gave the credit to Enma only, and that the sword managed to injure Kaido and give him this scar for life only because the sword is that powerful, then Oden's hype went to garbage as well.
So, if I was a writer, I would give balance to this argument and give credit to both and would point out these points:
1- Enma sword would NEVER hurt Kaido, UNLESS the user can apply this advanced armament haki technique to damage Kaido, this part of argument kept the hype around Oden's own skills to be able to damage Kaido regardless of what sword he got.
2- HOWEVER, the scar would ONLY remain perminent on Kaido's skin (which some claim to be immortal) only because the Enma sword has a special power that prevents the scar or damage from getting healed!
That way, Oda gave the full credit of damaging Kaido to Oden's skill, but at the same time, maintained the hype of Enma by saying its power counters something like immortality where its damage is perminent and cannot be healed
Again, it's all speculation hahahaha