For those using the Term "Base Luffy" & "G4 Luffy"
Yes, Gear 4 would make Luffy Stronger & able to do much better against Kaidou, but if he does that, it's a Certain Defeat for him, because
Gear 4 consumes All of his Haki, and pretty fast
Kaidou is simply Extremely Tanky. In such a Fight, Gear...