Story telling at it's finest. Luffy is 100% above Kizaru with no G5 time limit. This situation is just like with Cracker where Luffy is clearly is stronger but because he has a time limit he needed to be protected. Whole forum was arguing about how Cracker is clearly stronger and he got taken out with a clean hit. At the end of the day Luffy is a monster, this actually does not make Kizaru look bad. It's common sense that everyone fights differently. Kizaru is not a tank like Kaido, neither does he have Akainu attack power. Maybe if he focused on Luffy he would not have gotten hit in the first place because his fighting style is clearly similar to that of Cracker. If he knew Luffy had a time limit he should have paid attention.
Anyway looking forward to Kuma showing up at the end of this flash back. I feel like he might die though.