Oda made it clear since 2016 that Luffy's raw power was already at the peak of the One Piece world. That's why he said I don't want Luffy to beat Kaido "just
because his punch is so strong."
What was the solution? Stop focusing ONLY on raw power, and use advanced CoA: (as Hyo mentioned "you're using
too much brute strength")
Boundman Luffy's strength alone was comparable to a weakened/retired Garp or Sengoku strength + Haki. Not enough for Kaido. He needed advanced CoA + Boundman strength.
But again, as made clear by Oden in this chapter, he will achieve a >= Yonko level feat, not just Low Admiral level.