Whether at Whole Cake and Wano, he had a much bigger highlighted than Smoothie, a YC2, while he is not even Sweet Commander. I'm having trouble understanding the hierarchy...
Well there aren't any strong opponents to take her on.
IN wci, Luffy suffered against Cracker and won due to nami help
and katakuri it was like fight and run theory for luffy. he ran away mid fight.
sanji can't take on smoothi not because she is a women but because he was weak at that point.
and no one else was strong enough to take her on. if she were to come to onighishima. i don't think so minks or even neko could take her out. hence a bother to alliance. so oda probably decided to keep her out.
IN wci , oda didn't include zoro. he would have perfect match but in wano. zoro had his own enemy like kaido and king.