Yeah, you can call it a cheap power-up, you can call it an ass-pull, but that's your agenda and this is One Piece. Luffy learned FS from scratch in mere hours.
The fact remains that Zoro has CoC coating, and it's canonical, whether you find it cheap or not, and I've already tossed evidence at you as to why. You finding it asspull doesn't mean it stops existing, m8. You're not the one who's writing this story, Oda is. Sanji could start using ACoC too next chapter, and it would be cheap and asspull, but that won't make it un-exist. Sadly our agendas and opinion don't mean anything.
Those who said Zoro used ACoC on rooftop were being fanboys, and that's similar to saying Sanji has FS because Luffy does. But watching Zoro visually use CoC coating (the same visuals that are using for NOTHING other than CoC coating) without even having his swords coated in CoA hardening is practically a proof of him using just that. This is not being fanboy, this is simply having eyes rather than being blind or daft.
What YOU are doing is being a downplayer and downright choosing to ignore what you see to satisfy an agenda.