1. Kizaru’s Logia powers have no time limit, allowing him to constantly use them, while Luffy’s strongest forms all have limits since they drain his Haki. It is also entirely possible that Kizaru is Awakened and we have not seen his strongest form, yet.
2. Kizaru can attack from long range with light lasers, and can also use slashing attacks with his light sword, which Luffy is weak too. Luffy can’t shoot projectiles, and relies on stretching his arms to use long range attacks. While Black Mamba has a chance to hit, especially with the added use of Future Sight, that leads us into the next issue.
3. Kizaru is faster than Luffy. If you think Gear 5 is faster than the speed of light, please just don’t post a response, I’ve got enough gaslighting and bullshit in my life. Kizaru speed rushed X-Drake so hard in Sabaody that Drake didn’t realize he had moved until Kizaru’s foot was kissing his face.
These three facts make it clear that Kizaru is at the advantage here. He is faster than Luffy, can hit Luffy easily from range, and, if necessary, can simply avoid Luffy by keeping his distance using his superior speed until Gear 4 or 5 runs out, letting Kizaru easily clean up a gassed, Haki-less Luffy.
If Kizaru fights smart, he can constantly attack Luffy, while keeping Luffy from getting near him. I expect Luffy to get at least a few hits in, before Kizaru realizes Luffy is physically stronger than he is, and that he needs to attack from range.
Luffy’s ability to turn the world into rubber during Gear 5 isn’t really going to affect Kizaru, especially since he flies by turning into light. It won’t give Luffy enough speed to hit Kizaru, even if he stretches the ground like a spring, or his body like a spring (once again, KIZARU MOVES AT THE FUCKING SPEED OF LIGHT, OKAY???).
Luffy COULD pick Kizaru’s lasers up in Gear 5 and throw them, possibly, or reflect them with his body, or the ground, like with Boro Breath, BUT, a Logia having its own element thrown back at it won’t do anything to hurt the Logia user. Freezing Aokiji, throwing magma at Akainu, shooting smoke at Smoker, all fucking useless, no damage is happening. Shooting Kizaru's light back at him might tickle him, or something, but that's about it.
The only way Luffy wins a 1v1 with Kizaru is if Oda just takes a hot steaming dump on this series’ power scaling and ignores Kizaru’s speed.
Luffy will damage Kizaru a bit, Kizaru will acknowledge Gear 5’s strength and avoid Luffy’s attacks with his speed and while sniping with light from long range, and once Luffy runs out of juice, some other person will show up to protect him, most likely Zoro or Sanji, or both.
Future Sight is key here for Luffy, but not a cheat code; Kizaru is a smart, seasoned fighter, and no doubt knows how to deal with powerful enemies using Future Sight to read his moves by now.
Besides, Luffy reading his moves doesn’t matter if all Kizaru is doing is using his Light Speed to avoid Luffy, Luffy still can’t hit him. As long as Kizaru outlasts one Gear 4 or 5 in a 1v1 with Luffy, he wins. And, Gear 2 JUST ISN'T getting the job done against a Navy Admiral; even diehard Luffy fans that chew on condoms for fun should be able to admit that Luffy can't win without Gear 4 or 5 against an Admiral.
Kizaru low diffs, and it will be messy. Now... onto...
The Kaido Problem
BUT COC, DOES THIS MEAN KAIDO IS WEAKER THAN KIZARU???
Lol, no, because:
1. Luffy did not fight Kaido in a 1v1, he fought him after the Scabbards injured Kaido multiple times and cut into Oden’s scar, then with Law, Kid, Zoro, and Killer all getting good hits on Kaido (especially Zoro with Adv CoC, then Law and Killer with attacks that strike internally). Yamato also came to his aid later, doing damage to Kaido as well with her Adv CoC and powerful Mythical Zoan as she held off her father for a good deal of time.
While the Scabbards; Kid, Law, Zoro, and Killer; and Yamato most likely didn’t do nearly as much damage as Luffy did, what matters is that they allowed Luffy to rest and have time to come back.
Luffy fainted during combat after his first Gear 4, which would have allowed Kaido to kill him.
Luffy fainted after being attacked in a 1v1 clash with Kaido, meaning that, before unlocking Adv Conqueror’s Haki, Luffy would have lost VERY EARLY ON in a 1v1 with Kaido.
Luffy then fought Kaido until he was knocked out by Kaido, and sent into the ocean, where Kaido was then stalled by Yamato. If not for Yamato, Kaido defeats most of the Alliance by the time Luffy gets back up to the Roof.
Luffy lost to Kaido in 1v1s twice in this arc (not going to count the third time with CP0 Agent Guernica for obvious reasons).
LUFFY WAS ONLY ABLE TO BEAT KAIDO BECAUSE OF OTHERS, PERIOD. In a 1v1, a healthy Kaido would still destroy current Luffy.
Once again, Luffy’s strongest techniques are full of cooldowns that leave him weak, which Kaido does not possess. Luffy would still need others to buy him time if he were to fight a healthy Kaido again, if he wanted to win.
2. Kaido is a suicidal drunk and Kizaru is a hardcore, serious man who follows orders near ruthlessly at times, unless they contradict his personal code.
Kaido wanted to die. HE WANTED LUFFY TO BEAT HIM. Kizaru has no desire to die, nor any issues we know of killing Luffy.
Kaido gives his enemies chances to hurt him. Kizaru will not.
Luffy never fought Kaido at his peak. He never fought a Kaido that was motivated and satisfied with his life. As far as we know, Kizaru seems satifised with how the Marines do things, and has none of that baggage.
Kizaru will not start drinking booze or drunk ranting in the middle of the fight. He’ll make some cracks, but, he really is trying to kill you.
If Kaido fought Kizaru in a 1v1, Kaido wins, because he has Future Sight, Adv CoC out the ass, incredible durable and regeneration, and long range elemental attacks that can at least disrupt Kizaru’s movement.
Kizaru is just a horrible match up for Luffy, honestly. Let's see how wrong I am!