@theackwardstation:
Well, honestly, I think OP is very "loose" in some matters, so I don't really make too much of an effort to have rationalize this kind of stuff. That said, I'll give my 2 cents.
Sanji's fire powers don't need to come from genetic manipulation like happened to his brothers. In fact, I agree with you that it didn't need much of an explanation for why Sanji could do Diable Jamble, and Oda did initially explain it as friction caused from the spinning, therefore not as something innate in his body, although everything was a little weird.
However, this initial explanation seems to have been abandoned after the time skip, when Sanji stopped spinning to use Diable Jamble and could use over the top fire attacks like Hell Memories. That could be just a cartoonish evolution of Sanji's control over his technique, but perhaps Oda had new ideas for his powers. I wouldn't be surprised if his fire powers are indeed genetic.
imo i always think it has to do in PS with Sanjis anger(Heart) now more than anything
Emotions give characters abilities in OP it seems like Zoro and using fear to paralyze Monet.
I'm this makes sense. As u said OP as a verse is very loose and it the series combines mutiple different types of powers u see from cartoonish, gag, typical Shounen etc..
Only thing in OP that isn't "loose" is those extreme type of powers(gum gum, Mera Mera etc) hence DFs or other special means (racial/clan exclusive abilities, ancient weapons, special items etc) are for that.
Speaking of which, I know Some people who also don't like it, that Sanjis fire isnt backed by some energy source(it's not related to Haki) For me it's whatever I'm cool either way Op as a verse is very loose and unrestricted and thats why I'm such a huge fan of it's systems. As compared to series that have it that are opposite and limit it to only 1 source(ex Naruto with chakra).
But maybe that's cause im just fatigued of the energy Monopolizing series like Naruto , Bleach, DBZ(not that they are bad) I just prefer OP more open system altho the series has Haki, plus there DF which they makeup the majority of sources of powers for characters. But they are not the end all be all like Chakra(Naruto) and Reiatsu(Bleach) and Ki(DB) is
But DF and going forward as we learn more about Haki, they have the most potential to make u powerful and take u at the top.
Sorry for making this post long, just had alot to say