You're misinterpreting that line, "a knife is a chef's soul", a chef main tool is his knife, how they cuts and prepare their ingredients is important to them, sanji highly value foods and never waste them, that's why it's call the chef's soul, cause everything starts there. In Japan cutting meat is like art form, they don't just butcher it like an animal.
If he doesn't have coc and if it's part of the process then there's no way sanji can tame enma let alone weild it in a fight. By your admittance he has yet to show coa not to mention ryou.
Sanji taming enma is a pipe dream.
Just because zoto can do it doesn't mean sanji can as well.
Hitetsu stated that no one before or after oden had succeeded in taming enma, I don't see why kyoushiro should be excluded from that list just because he was not present at that moment. And if we add coc in the mixed it becomes null and void to argue for kyoushiro since he doesn't have it.
Granted it may not be canon but is coming from the perspective of a renowned author of FWs
zoro's said the following "Chefs and swordsmen make their living by the blade"
its not about the technique a chef uses but the relationship between the chef and the blade that pulls through at the end of the day.. calling it a companion would have been mild but calling it one's Soul is just like zoro said "the blade understand my will" that kinda relationship..
tho i agree with you on the Coc part.. but a still bit hazy with that whether its a necessity or just a leverage like i said
sanji has shown Coa and has been called out for using it in certain occasions as well..
i honestly dunno about Ryou.. it seems like enma grants that to zoro.
and
..DJ is still mysterious.. some
say the fire is haki..some say its Coc.. bruh there is alot unknown to really conclude anything..
what i claim is obviously an assumption based on my gut feeling of sanji's capabilities regardless of what he has shown.. i believe you need strength and i believe sanji has it..
ii get when you say people blabber about "if zoro can do sanji can do to" when in reality zoro did nothing but get enma to succumb to his will and strength.. which may or may not entail Coc.. (which is likely he did) but is it a necessity i don't reckon.. it certainly would be more difficult for sanji seeing how he isn't used to katana's grade .. and he prolly wouldn't even bother noticing enma..in the near future
as for his potential if he decides to become a swordsman.. i believe he can.