Zoro implied it with his own words this chapter.
Zoro will surpass Oden when he blackens Enma.
Zoro will surpass Oden when he blackens Enma.
1 - Kaido was in hybrid form
2 - Zoro was having a constant fight with Enma
3 - Zoro had insane injury prior to Asura feat
Now tell me, how insane would be Zoro asura vs Dragon Kaido with a full health bar and a complete understanding of Enma (not blacken yet). Well I leave it there for some argument