1.) Although yes your point about Hiyori is fair, Kawamatsu raised Hiyori so why shouldn't Kawamatsu be the one to defeat Kaido, going by this logic? As for Kuina, she until proven otherwise has no connection to Wano, nor does Zolo himself. Why would Ryuma give Zolo motivation to defeat Kaido? As for Yasui, Zolo was angry at Orochi for Yasui's death, not Kaido. As for O-Tama, Luffy is far closer to her then Zolo is so if anything, O-Tama is just another reason why Luffy should defeat Kaido and not Zolo.
And it's not like Zolo would defeat Kaido on behalf on them, anyways. Zolo's priority, just like in every other major fight he has gotten in since the very beginning, is chiefly for his own progression as a fighter and to fulfill his own blood lust for combat. This is why when telling Queen he would defeat Kaido, Zolo immediately mentioned Kaido's strength rather then his cruelty towards the people of Wano. Kaido is just another challenge for Zolo, nothing more nothing less.
2.) It really isn't that shitty though, Luffy was dealing damage and tanking hits from Kaido even before he got his CoC bloom. In Base Form, at the very start of the fight, he literally ate a Thunder Bagua and took barely any damage, so him getting up from a Ragnarok after getting knocked unconscious temporarily shouldn't be that much of a stretch. As for him fighting Hybrid Kaido evenly, I mean, all I have to say to that was that it was inevitable that a CoC specialist like Luffy would be much stronger once he learned advanced CoC. It's the rarest and seemingly most powerful varient of haki, so the advanced version of that should warrant a massive boost in power also.
3.) "they were unsure"
1 single Shigan and Zolo was coughing up blood and face-to-the-floor
Same with Luffy, one panel later and they all the way across town. It was a neg-diff through and through, they took a shigan + unnamed kick and they were thrown across town like trash. Seriously man go watch the anime or something it was the most neg of diffs ever LOL, their attacks did 0 damage and they couldn't do a thing, yet later that day they beat them anyways. You want to talk about Luffy's ridiculous progression? He always progressed like crazy.
4.) "Luffy not owning up to his mistake = trash character" Would Luffy have been a trash character if he sat by and ignored Big Mom's threats toward Fishman Island? It's within his character to threaten those above him in power, him threatening Big Mom is no different. She will get defeated when the time is right, as of late Big Mom has been easy to deal with, don't forget even Robin was capable of displacing her from combat.
5.) "He had answers for all of their attacks without resorting to guts or natural df causes." Doesn't matter who uses df, Law isn't any less impressive then Zolo because he has a devil-fruit, you targetting Luffy and other df users just shows your bias once again. Zolo has been useful on the rooftop but besides carrying Luffy, he has mainly just been a damage dealer just like Killer and the Scabbards. Any damage he has done in this fight pales compared to Luffy anyways, I mean the guy in his strongest form couldn't even make Kaido fall, something even Luffy could do even before he got his haki-bloom, Luffy in his Kong-Gun Gatling had Kaido knocked Kaido out for a short period of time.