I think that's too complicated and doesn't align with the fact that Oda retconned Tekkai as Haki.
It seems pretty straight forward though.
Haki is the manifestation of one's Spirit.
Sanji's passion burns hotter than fire, so his Spirit manifests itself as Diable Jambe, but since his CoA is lacking, it gets held back.
A lot of Zoro's attacks seems to manifest into shape, which could be contributed to the intimidation factor he has going on, so his Spirit manifests via the mind creating illusions, but since his CoO is lacking, it gets held back.
The stronger they become in the form of Haki they don't specialize in, the stronger their abilities become.
I don't think that's overcomplicated, because it fits the narrative pretty well, and offers some real depth to Haki, and these guys growing by EoS.
Cause lets be honest, where do they powerup from here?