Luffy will do some damage to Kizaru if they fight.
But, if it's a pure 1v1, once Luffy runs out of Gear 4 or 5, Kizaru will stomp him. So, the question then is, can Luffy beat Kizaru by wearing him down in Base w G2 and G3, and then using G5, or, will Luffy be unable to keep up with Kizaru without G4 or G5?
Vegapunk knows Kizaru well, and has studied his Fruit, so Luffy might have some help here.
Luffy isn't ready to win a 1v1 against a top tier with no help whatsoever.
His strongest forms having short timers and brutal cooldowns just hurts his endurance in ways he can't make up for yet.
Luffy needs to learn better Haki control (most likely from good ole Shanks).
If Luffy ends up in a 1v1 with Kizaru, he will need to be rescued, by either Zoro or Sanji, or both, IMO.
And then this guy does... something...