Seems like fools have already forgot how GK works.... Not sure, but I dnt think anybody claimed it would instantly put Kaido down. Considering that Doffy himself was still kicking a bit after it.
But the initial AP behind GK, only the first part of the attack. The truely deadly part of the attack the overall after effects. Law even notes killing him irrelevant, doffy as good as dead regardless what happened to him.
Doffy obviously countered it, but unless Kaido legit counters It. I’m expecting this to come up during then fight.