Some still don't get it. Putting everything into an attack at 30%, 20% or anything less than 100% doesn't equal to putting everything into an attack at 100%.
A character's strongest attack will always be their strongest attack regardless of their condition. Strongest attack at 100% is stronger than strongest attack at 40%.
Zoro still outperformed Luffy. Luffy has been knocking Kaido around since they first fought and received a power up and he still haven't done any significant damage to Kaido.