You can try to pretty up as much as you like. It's not sanjis fault. It's his stands fault for thinking he was incredibly special on his own merit. And that's what's hurtful. Him being strong would have literally been solely because of his dad reengineering his genetics
Dude , I dont know what you are talking about.
Till now , sanji did not use any modifications factor. And stronger than his siblings. To create diable jamble till PS , he needs to form high speed with his body. And after ps , haki ability help to create diable jamble directly .
Also , I see your attempt. Just you are trying to say how can sanji be strong so much without any training. But facts are not those.
Everybody is special in OP.
Check Luffy family and D .
Check zoro family who are known best swordsmans.
And oda can select this way for sanji. But idk why you are trying to see different . As a essential , totally same thing with others.
Sanji has own will and decisions .
Odas answer would be enough . He is using fire with his burning heart. ( emotions )