You idiot, if Sanji with regular flesh body can bend doors. What will Sanji with a an iron body kicks would do. Think Judges son
basically nothing significant it will just be another hard kick..
Doffy literally says to Luffy who using hardening to hit him that he's fast but has no weight to his punches..
so hardness is a negligible factor in AP.. its the force mainly making use of that hardness.... and iron club tot hr face would feel like a steel club to the face for the same reason.. its negligible to distinguish the which one's harder since they both hit and hurt.. what matters which one lasts or is more durable thats what the term harness is for
now that i legitimately give you LUFFY's case of hardening bazooka doing not shit to doffy coz it has no weight to it. the same Luffy who one shot Ted a pacifists with a jet pistol no hardening
so.. hardness barely does shit if the force entailing it or the "weight" isn't making use of it..