Im baffled at your double standards.
Luffy’s haki upgrades have nothing at all to do with his devil fruit
Sure, because you conveniently isolated only Luffy’s Haki upgrades. His biggest Wano power-up was Gear 5, the awakening of his Devil Fruit.
So pick a comparison.
If we are comparing Haki development, Zoro learned CoC coating, Sanji did not receive a Haki upgrade, and Germa is irrelevant.
If we are comparing their overall power-ups, then Luffy’s Devil Fruit, Zoro’s Enma and Sanji’s exoskeleton all belong in the discussion.
You keep using the first standard for Luffy and the second for Zoro and Sanji.
Zoro is a swordsman. Every offensive Haki application he develops will be expressed through his swords. Luffy applies Haki through DF body: his punches and fruit-based forms because that is how he fights.
What would satisfy you here? Zoro throwing Enma away and punching King so the Haki can count by itself?
Zoro just has a stronger version of haki he already had because of enma
Enma forces Zoro to release more of his own Haki and control the output. That is an improvement in output and control, regardless of what triggered it.
You are treating Luffy improving his Haki through training as Haki development, then treating Zoro improving his Haki through mastering Enma as nothing more than a sword upgrade…
Sanji still only has basic armament but he stacks it on top of his new exoskeleton
Then Sanji did not develop his Haki through Germa. His body became tougher and he combined that toughness with Armament he already possessed.
Once he fully accepts himself for everything he is he’ll likely finally unlock conquerors
SAnjis conflict with Germa is real, but the claim that accepting his Germa blood will unlock CoC is still your theory.
Gaban told him to become a king. Nothing in that scene established Germa as the source or trigger.
In Zoro and Sanji’s cases it’s extremely in your face
It seems obvious to you because you started with the conclusion that Luffy represents Haki, Zoro represents swords and Sanji represents science, then sorted the evidence around it.
The data does not give you three routes.
Luffy uses Haki through brawling and his Devil Fruit.
Zoro uses Haki through swordsmanship and his blades.
Sanji uses Haki through martial arts, Jambe and his modified body.
Luffy is simply the most advanced Haki user among them. That does not place his Haki outside his fighting style while everyone else is defined by theirs.