Imagine back the force Kaido had smashed on those 3 idiots who carelessly talked about 'not to underestimate the SH'. That was not imbued w/ haki---pure raw strength. If haki can make someone many more times stronger, how do you expect Luffy to defend againts it? Now, it's clear that we don't have an ending in which Luffy is the PK. Periods!!!!