While it's true Luffy couldn't hold a candle to Kizaru until G5, Kaido was actively hurting G5 while consistently taking damage from it, which is something Kizaru couldn't pull off so far. The most he managed was a stalemate—and it's a plus for Kizaru in its own way given his fighting style.
Kizaru is a swordsman after all, as much as people want to deny it but his results speak for themselves.
His CQC result is exactly like Zoro's - they never get hit cleanly.
So it isnt fair to expect the same from Zoro and Kizaru type of fighters what you expect from Kaido and Luffy type of fighters.
Swordsmen are too good in CQC to be hit while Kaido and Luffy easily get smacked over and over again.
That's why swordbois rule supreme and a fight between a swordsman and brawler is nearly impossible.
That's why Kizaru resorted to his sword the least so Luffy could stand a chance.