Agenda aside ultimately oda places the narrative above powerscaling. He thought “well it would be cool to Ace like Luffy beat a warlord” and then down the line thought “hey this guy is king of the lizards, Kaido is king of the beast, it would be cool if they’re were rivals turned allies”
I bet you he did not once thought this would make Ace look extremely strong or Kaido weaker than portrayed. He just thought narratively speaking it looks good.