plot is not a detailled explanation now is it. try again. if you can, that is.
it doesn't matter what I explain...I ain't Oda...he writes the "plot"....you can give all the detailed explain of anything that will happen in the future based on past events....it doesn't change anything even if you make 100% sense when Oda doesn't go that way...
even then, if you want few I can give you...
King "the wildfire" is his epithet....so I assume he has some fire powers....Sanji with RS is fire resistant...so it won't effect much...then he left with swordsmanship and his Zoan powers and haki.....
King is speedster and so is Sanji and RS gives him durability, invisibility and probably it increases his attack power.....also, Sanji's CoO is good enough to evade critical hits
Now, we haven't seen full powers of his raid suit....furthermore, we have yet to see the power output of combined DJ+Hell Memories + RS......
though it was not show, there is a possibility of modification of RS and he may have trained his haki further......if he is clever enough that he was in alabasta or EL...he may device some traps against fighters like King to take him down.....afterall OP has proved many times that you need not to be stronger than your opponent to take him down......