You know, I just came to relize that Luffy is not as compatible with the entire style as people are claiming that he is, mainly because of tekkai. Since tekkai is a muscle condensing technique, Luffy's muscles are rubber and thus unable to use the technique properly, but thanks to being able to use CoA to harden his rubber body instead, he won't need it.
Luffy's muscles work like everyone else's: They contract. Thus, Tekkai works for Luffy.
Muscles are naturally flexible, so saying flexible, stretchy muscles prevent them from working well is flawed logic.
As for Robin, I think her abilities work well because of her concentration capacity. She could only keep Cien Fleur Wing for 5 seconds because it's too much stress on her mind. Naturally, if she forms multiple legs for Rankyaku, that will wear her out even faster.
So if Robin ends up using up her mental stamina forming high-powered attacks, she better be sure she hits them, and that they aren't defended against or countered.
Multiple Shigans vs 1 Kami Ei? Multi-Rankyaku vs Soru? The single moves just work more economically, while successfully defending against the multi-attacks.
Compared to Califa, I don't see Robin necessarily being better. Califa has soap that weakens opponents' muscles substantially. Sanji was rendered powerless, not just because Califa's sexy.
As for other Strawhats, they've already found ways of fighting that makes at least 1 form pointless.
Sorry for being a snarker.
It's how I roll. I simply find it hard to relieve stress during Finals week.
However, your huaquandao and Rokushiki Robin projects are creative nonetheless.