In an older databook, Luffy and Zoro were on the same Strength level
What you mean the strength=6. C'mon you can't be serious?
You have Oda stating otherwise at least 2 other times. The fact that Luffy is the captain of the crew should be enough to tell you that but your going with strength level 6 as your argument?
We see Zoro use his strongest attack along with a completely new CoC ability he just unlocked only to have minimal affect against Kaido.
Then you have Luffy use AdCoC in
base form challenging Kaido for an extended period of time and actually make him reel from his attacks. You really think they are equal?