High difficult?
Zoro has been fighting none stop since he found Luffy. He could not take more than a step without someone attacking him. There are a lot of opponents. In fact, Oda told us the number of Gifters, which is 500. That suggest Zoro will face and beat all 500. It's takes time to defeat those numbers. We have not seen him use a high level attack. Just him normal none name attacks.
Zoro has been fighting none stop since he found Luffy. He could not take more than a step without someone attacking him. There are a lot of opponents. In fact, Oda told us the number of Gifters, which is 500. That suggest Zoro will face and beat all 500. It's takes time to defeat those numbers. We have not seen him use a high level attack. Just him normal none name attacks.