Did you forget Alabasta where Zoro seemingly unlocked CoA and CoO, which later went on to become the basis for cutting steal? Literally came out of nowhere. Haki hadn't even been explained in the slightest at that point, yet Oda gave it to Zoro on a whim.
And Luffy had already mastered the basics of Haki. It was already explained that Haki blooms in extreme circumstances which explains how Luffy went on to unlock the advanced forms. What happened what Zoro was pitted against Kaido? AdCoC outta fucking nowhere, without a shred of indication that he could even use basic CoC.
Zoro didn't unlock CoA in Alabasta, you can make a case that Zoro did unlock this specific use of CoO in Alabasta, after he was shown that was possbile and taught that by a master as a kid, and that only happened because he was in death's door and remembered that moment, and if it's confirmed Asura is CoC and that he used it even before Luffy, great then, i take my L here.
But even accepting all the Haki awakening stuff for both of them, doesn't Luffy still have Gear 2nd, Gear 3rd, Red Hawk, Voice of All Things and now something special about the DF that for sure is gonna happen by the end of the series? awakening or something specific about the Gomu Gomu, i hope it doesn't, but i do think it will, you don't think it will?
just looking at these things, Zoro still has a more realistic power base because of that, because even his crazy power ups are constant with Luffy's realated to Haki, but then Luffy get's more crazy power ups that have no sense on top of those related to Haki.
And even then Luffy's Haki crazy power ups are more nuts than Zoro, because when Zoro gets awakening of the basic CoO / CoA in Alabasta like you said, Luffy is out here getting advanced observation, advanced conqueror's and the only one he learned by training was the advanced armament.