When the CP9 were introduced they were framed as a killer elite, the best assassin squad the WG had ever seen, the most physically formidable foes the straw hats had ever faced, due to a from-childhood martial arts training regiment that had pushed their bodies "beyond human limits", manifesting in 6 to them unique superhuman martial arts skills, including the troublesome ability to harden their bodies. Jabra is framed as uniquely skilled in this technique among them, being able to use it and move. The versatility and strength of their martial arts is a cornerstone of what makes CP9 fearsome to the crew and revered among their peers.
Also worth noting, before the time skip armament haki is, once introduced, used for bypassing DF defenses, never as a skin-coating literal hardened armor.
But now, post skip, in order to retrofit haki properly and make things Make Sense we must recontextualize CP9 as comparative greenhorns, lacking in the basic, foundational fighting skills of every single worthwhile post-skip combatant, or maybe them being complacent and NOT training in skills that would, say, allow them to kill a DF using target and when you think about it they probably only ever killed normal people yeah, and after all the REAL tough assassins are in CP0 which was definitely always a thing…but then you're gutting the CP9 of everything they represented in their original appearance. All the stuff about them being the revered, most fearsome ever superhumanly trained martial arts experts go out the window. One of the cornerstones of their moveset becomes a subpar variant of a skill everyone can suddenly do, and weirdly Jabra becomes the only one among them who can apply it in the most rudimentary manner.
It’s a case of “if haki was always a thing and CP9 had haki all along why make one of their 6 cornerstone techniques a worse version of armament, and why did they never do [X, Y and Z]” and “if haki was always a thing and CP9 never had it, why the hell not and what does that make of their reputation”. The depiction of CP9 worked 100% in and of itself in their featured arc, and trying to retrofit haki onto them either doesn’t fully work, or goes against their original depiction.
This whole thing reminds me of how people will insist chapter 1 sets up Conquerors haki even though the Shanks/Lord of the coast sequence made perfect sense from day 1 in and of itself and doesn’t really work like CoC anyway – Shanks gives the Eel a really mean look and tells it to piss off (neither of which need be associated with CoC usage at all), the panels soom in on Shanks really intense glare to drive this home (again, irrelevant to CoC usage but ABSOLUTELY relevant to making Shanks seem intimidating), and the Lord of the coast goes Gulp and bolts (it doesn’t faint). Theres no sign of any sort of force emanating from Shanks or affecting anything, like when he boarded whitebeards ship.
Like, its so simple, Shanks looks really intense and the Eel gets scared and takes off, its absolutely useless as foreshadowing for King Haki. And Yet. Idunno, maybe that high enough haki levels to not faint or something, and Shanks was focusing his haki in his eyeballs, He was not as skilled back then so he also needed to be mad for it to work and and and…
I get the desire to have it all make sense and find clues that masterplanner Oda master planned this all along, but when the original scenes are perfectly self explanatory and understandable within their own context and aren’t framed as if to draw attention to novel, future concepts 100s of chapters before they’re relevant, and if they don’t fully adhere to the rules of [future concept] anyway visually or functionally…rather than trying to retrofit them as super duper secret foreshadowing Its just so much simpler to go “Oda probably hadn’t developed this concept 441 chapters in advance.”
–- Update From New Post Merge ---
@FolhaS:
That was indeed one of the scenes I was thinking of, but after review Luffy doesn't actually say anything, he's just badly and strangely hurt by a physical attack. That along the super attack Wolfwood also mention, and Garp's fist of love felt like hints to some types of strenght that could hurt even a rubber man.
Him being badly and strangely hurt is not really evident or emphasized at the time, Its something that is brought to the table in retrospect. The scene explicitly zooms in to highlight that the shigan interacts with Luffy as if he is rubber, and then Lucci goes “you’re lucky your rubber”, and Luffy is uncomfortable because even a rubber man does not enjoy getting his trachea smashed. If we were meant to take special note of it Oda would’ve written in Luffy or his friends or the CP9 doing just that, like when Garp punched him. The Rokuogan move was explicitly said to work like an impact dial, something that was well established as capable of hurting Luffy. In the Skypea arc as well you have Enel batting Luffy around with his staff and restraining him by pressing it against his throat, which again Luffy all clearly finds uncomfortable. Luffy then affirms that such moves can’t truly hurt him, but that doesn’t mean Oda wont draw such moves as annoyances to suit his needs – having Luffy be blassé and oblivious to any such blow pre-skip would rob a lot of scenes of their tension, and having every single attack directed at Luffy be a blade of some sort is a LOT of hassle.