In Luffy's defense, Luffy is holding on to Kaido to launch his final attack, and this attack from Kaido is actually much more focused than those he used before, which are randomly sent in different directions without aiming at a definite target. However, anyone who denies G5 Luffy is failing to dodge attacks that wouldn't even touch him outside G5 is definitely not paying attention. I am not sure if it's because Luffy lost the sense of danger due to Nika's influence, but G5 Luffy's reflexes are nowhere near as good as they are outside G5.