They did make Sanji's RS with him in mind for whatever reason, so it's possible it has unique features that take into account that he's unmodified unlike his siblings. Other RS' may also have unique abilities but I think what's unique about them is instead boosting their user's pre-existing genetic powers.
I agree that the Diable Jambe looks like the result of some sort of genetic power, but at the same time it doesn't.
The first time DJ was introduced, it was justified as "Sanji spinning on himself so fast that his leg bursts into flames (that for some unspecified reason don't hurt him despite how devastating they are against his opponents)". DJ bothers me a bit because of how illogical the skill seems, but it was introduced at the same time that Asura and Gear Second, two other techniques that bother me just as much for the same reasons. Asura is just as illogical as DJ, and even more unexplained than it. Also, now Sanji seems to be able to go DJ without spinning first, as if he had instant combustion powers, but Luffy also somehow turns G2 without first pumping the blood inside his body through his legs, which should be compulsory to start the power-up. Post-TS Luffy is even somehow able to use G2 on localized limbs (instead of the whole body), which makes absolutely no sense because of how the skill is supposed to work.
What I mean by that is that despite DJ not making that much sense to me, that's fine, because the power-ups that were introduced at the same time as DJ for Zoro and Luffy make just as little sense and DJ so it's probably not the result of unique genetics but of foggy writing.
