It is just base attack, duh.
King have aerial advantage, the BM's ship arent even land on water when the attack happen, duh. It is the same when Marco kick Kizaru in mid air, Kizaru cant dodge it. Anyway beside Big Mom, all of them are fine including chess soldiers. Do you want to say King insane attack cant injure chess soldiers?
Big Mom want recruit him because he is one of the race that BM dont have in Totland, and he is the only one left, duh.
BM is Kata's fucking mother, what do you want him to do? Spitting BM's face?