I'm just gonna say one more sentence on the matter: If we see Zoro lose his muscles and strength to the point where his arm looks bony, and his arm has Haki unintentionally activated, then see him will both back to his own body, I don't see how it is up for debate.
@Calaca - Newer abilities such as potential energy-related and shockwave manipulation have not been added to the haki page (last I checked, especially since now we're discussing new potential abilities pertaining to haki), and the format should likely be changed to list each ability type, and have the magnitude (inept, adept, proficient, advanced, etc) listed under instead of current, as Fix pointed out that simply listing the page for Haki does not provide sufficient detail for each character's usage of Haki.
For example, we'd have Zoro be competent with transfering his haki to other tools such as his blades (via a more "basic" application of Goken), and being capable of using Statistic's amp via Koka quite proficiently, but he's never shown Precognition (unless the fight w/ the angler fish suggests as much in the manga), but is known to have some level of Extrasensory Perception with Kenbunshoku.
Luffy on the other hand as quite a number of feats. He's advanced in Extrasensory Perception for Haki, and at least proficient w/ Precognition after his fight w/ Katakuri. He's also now an adept user of Goken to the point where he can comfortably use the advanced application without much strain, but we've yet to see him EVER transfer his Haki to other objects (I forgot if he actually did so to his sandals in Gear 4th at some point, but if not, then yeah...)