Reiju was able to develop emotions yet she can't use fire.
That's now how it worked at all.
The fact that the germa siblings dont have emotions, doesn't mean they dont "feel".
Reiju was able to becomic someone with empathy, because she was raised by Sora. She has the same modifications as the others. Sora's love was able to counter a bit of the "no heart" thing, but Reiju still can't disobey Judge.
When the quadruplets are born, Sora got ill because of the drug. The drug managed to put Sanji's modifications into a dormant state, that's why he never developed the exoskeleton, strenght, or "no emotion" thing.
But the difference between Reiju and the triplets, is that they weren't close to Sora as she was. Sora was too sick to raise them and died soon. They were raised by Judge alone. That's why they grow up being absolutely dicks, thinking they are better than everyone else etc, because those were values taught to them by Judge.
But just like Sora's love was able to counter a bit of that for Reiju, Sanji's decision to save them at the wedding also served as a catalyst to do the same for the triplets. That's why they decide to save him in the end. Also how they would decide to go back for Niji and Yonji. Before they would have accepted their capture and leave, just like they accepted their death at the wedding.
So, the Raid Suit broke that "dormant" state and made sanji able to activate his latent abilities, but since his "love" is too "Strong", the "no heart" modification is never able to dominate him (at least not easily).
But DJ was before that. Sanji becoming a powerhouse was before that.
Sanji grew strong when raised by Zeff, his adoptive father. Sanji stated multiple times that his "love" or "passion" burns hotter than flames, etc.
And we know "power of love" is an actual thing not only because of Garp, but also because of the Buccaneers.
Schooled.


