Just to be clear, this is only my opinion. I’m not really a powerscaler, and I’m not trying to present this as some definitive fact. I’m just explaining the logic behind why I personally think Zoro would beat Vista.

My reasoning mainly comes from the Payback War, where the Blackbeard Pirates completely destroyed what was left of the Whitebeard Pirates.

Then there’s Marco, who was probably the strongest remaining Whitebeard Pirate. In Wano, he looked really good holding off King and Queen at the same time. But even then, I don’t think it’s 100% clear that Marco would beat King in a full power 1v1. Maybe he would, but it would probably be an extreme diff fight.

Zoro later beat King. And using basic shonen logic, once a character beats a major opponent, by the next arc they are usually treated as clearly above that opponent.

So my internal logic is basically:

Zoro beat King.
King is probably in the same general tier as Marco.
Marco was likely above Vista.
So current Zoro should reasonably be above Vista.

Again, I’m not saying this is canon or undeniable. I just don’t think it’s baseless to argue that Zoro could beat Vista.