Dude, it measures proficiency in Rokushiki techniques & physical strength. From OP wiki, it is described to "directly determine someone's level of physical power. As such, it also allows one to estimate the power of their Rokushiki."
Rokushiki are the martial arts techniques that CP9 used, which is why I said it measured "proficiency in martial arts skills that the straw hats themselves do not use." In essence, we would be imposing a power-level system that reflects the rokushiki master of the CP9 agents upon the overall fighting abilities/power levels of the Straw Hat crew, when they are not rokushiki users themselves.
Furthermore, I've only used information taken directly from the vivre cards, manga statements, and one piece wiki. On the other hand, your arguments are based on the notion that you can correctly deduce exactly what Oda was intending to convey through the use of parallels/dynamics/descriptions that require subjective interpretation.
Now, I'm not saying that there is no Zoro/Sanji paralleling throughout One Piece. There clearly is. However, to treat that as the end-all, be-all of all powerscaling discussions is objectively more flawed compared to direct statements from the author himself. And I say all of that without even mentioning any of the Luffy/Zoro parallels that present themselves in the story with similar prevalence.