So, here's an example of how durability negation/internal destruction with Armament Haki looks:
As you can see, his Haki touches and enters the tree, and it bursts from the inside. Basically, if Zoro's Haki, not his blades even, but his Haki, touches Garou, it'll be as if he was being slashed from
inside his body.
Also, the way that Armament Haki works is that the stronger individual wins. If Zoro has the AP advantage over Garou, his haki would likely effect him in that same way until he grows stronger (I say "likely" because the only time we've seen Armament Haki get overpowered by brute strength is when Armament is used defensively and someone overpowers it with brute strength).
One more thing. Haki isn't magic, it's spiritual energy. I don't know if Garou's dealt with anything like that or is capable of deflecting something like that off the top of my head.
Moving on from Haki, I'm gonna actually start talking about the combatants now. Off the cuff, Garou's Instinctive Reaction and Reactive Evolution will give him great advantages. However, Zoro has advantages of his own. Zoro's Ichi Ni Gorilla would boost his offensive power, as would Asura. Armament Haki also functions as a defense and offense buff, which would allow him to block more powerful attacks from Garou, and it also buffs his attack along with the added perks of dura neg and emission, which would allow him to increase the range on his sword swings.
Speaking of range, even if Garou made a decent amount of distance, Zoro outranges massively and could spam sword slashes that reach hundreds of meters while Garou's best ranged option (should it even get to the point where they try zoning each other) would be Whirlwind Iron Cutting Fist, which only reaches several meters.
Both these guys are built different when it comes to pain tolerance, too. Just throwing that out there.
I didn't cover Zoro's Observation Haki since I don't know if he's really done anything impressive with it (or shown it that much, for that matter) in the Wano Arc. I will say that what he has shown of it in other arcs, though, is that he probably won't get mixed as often by Garou should he try something like using Watchdog Man's movements, since his level of Haki would allow him to sense Garou's presence in his vicinity.
Not quite sure who wins, but I think I'm leaning a bit more toward Zoro.
Oh, and tl;dr Zoro's dura neg could probably go through WSRSF due to the fact that it's spiritual energy being sent into Garou's body that does the damage, and I don't think Garou resists that.
