We know too little of Smoothie in all honesty.
Bounty difference will be a huge suggestion, also, the fact she was stopped many times by Reiju and that she admits her inferiority to Katakuri, this tells a lot.
King is for sure a bit stronger than Queen, but the fact that Queen doesn't admit It means that he's not that from for him, like he isn't scared to fight against him and also King teases him saying "Jack was considered enough to leave, you weren't", but King doesn't talk to Queen like he does with Jack and that's because he actually knows, rivalry aside, that the Cyborg is strong.