sanji feat isnt impressive in itself, he hit nasujuro human body part with a direct attack, offcourse that was going to do some damage since it was nasjuros unprotected body part. brook and franky would have done more damage if they hit nasujuro with a direct attack to on his human body part. The hype with nasujuro can be resumed as this, his lower body part which is probably more durable than diamond, his swordsmanship which he didnt bother to use on sanji and lastly his immortality that make any attack irelevant and erase the weakness of his upper body part. So that is pretty much it, nasujuro hype is intact, sanji got some hype but was negged 0 second after. To beat nasujuro you will have to overcome his immortality/ice power+ swordsmanship/the durability of his lower body part something only the futur WSS can do.