if this is an old idea i apologize…it just came to mind reading chapter 513 since it seems Rayleigh is a swordsman and was Roger's 1st mate.
also...why is everyone against the most powerful people having DF's? its not even clear that Mihawk, Shanks, and WB don't have DF's...
what is with this nonsense that DF's are cheating? its being revealed that more and more of the big players in the OP universe are DF users so i wouldn't be surprised if all of the big players had a DF. More DF's actually make the story more interesting, because the power scale in OP isn't linear...its like rock/paper/scissor and totally unpredictable.
btw, for the record..i think Rayleigh is just a swordsman and has a seastone sword...gives hope that in the future Zoro will get one and be able to tackle logias...and maybe Sanji can get Seastone shoes or spurs or something and do the same.