Ryou is just armament haki. The question isn't if Killer's haki is strong enough to cut steel (that's pre-timeskip Zoro stuff), it's if it can cut Kaido. Killer getting beaten by Kaido before is meaningless since you have no evidence that he put up an actual fight. Hawkin's literally calculated the chances of them winning at 0 so where did Killer cutting Kaido come from when none of us even saw that fight? You're assuming that based off nothing, Killer can harm Kaido but Sanji can't. How is Sanji not strong to be up there with the Worst Generation? He's the one who clashed with a Calamity and even earlier than that, clashed with Drake (no raid suit) and wasn't seriously hurt in anyway.