Kat can't handle a kick from sanji using ifrit.
Sanji just launched a 20 ton cyborg Dino across an island and a half. That far exceeds g4 luffy in physical strength in terms of feats
Add in the plasma heat aspect and the attack power is doubled
Kata got destroyed by g4 luffy in a couple hits. Sanji blitzes and neg diffs with 2 ifrit jambes
Sanjis faster than kata
Sanjis got better ap than kata
Sanji has better durability than kata
Sanji has better endurance than kata
Sanji has better stamina than kata
Sanji is all around better than kata and king and marco
Knockback of a
fainted opponent isn't everything, Luffy sent Wapol flying to another island in base 900 chapters ago, knockback counts a bit more if it is DURING the fight and the knockback itself is what is overwhelming the opponent, e.g. Luffy vs Doflamingo.
Kat got "destroyed" because G4 is an
extremely strong limit break technique, he was still hyped as undefeatable, where King and Queen were not.
Sanji doesn't have better stamina considering he just fainted after a shorter fight than Luffy vs Kat, and his armor/regen was
partially fake hype considering winch queen can bust through it.
Kat can casually make multiple superior to G3 level attacks with insane hardness sprout from anywhere and see ahead of time where you will be to perfectly hit you. Sanji's armor isn't at the level of blunt force immunity like Luffy so he will struggle with this.
Sanji is extremely strong and above King, but no way is he above Katakuri.